Fabric Face Masks: Cleaning and Disinfection

Reusable fabric masks should be cleaned and/or disinfected before each use to reduce risks associated with COVID-19 AND other potentially infectious microorganisms (e.g. bacteria, viruses, and fungi). Although the general principles of mask cleaning and disinfection are the same for most fabric masks, details will vary depending on specific mask designs, features, and materials. These details should be provided by mask makers, but for those creating their own masks or acquiring masks from nontraditional sources this may not be the case. As always, please check with relevant regulatory officials and manufacturer’s instructions! In this post, we provide an overview of fabric mask cleaning and disinfection methods such as washing, boiling, and steaming, with special attention to methods appropriate for spunbond nonwoven polypropylene (NWPP) mask materials:

Overview: A Practical Guide to Cleaning and Disinfection
Definitions: Mask Cleaning and Disinfection
Mask Cleaning and Washing Advice
Mask Disinfection Advice
Conclusion

Deeper Dive for Mask Makers: As part of the FDA’s latest guidance for mask makers, everyone making reusable masks for COVID-19 needs to include a label with “recommended cleaning and/or disinfection materials and processes”(see the FDA EUA April 24, 2020, and MakerMask post about labeling). It doesn’t matter if it is hand-sewn, machine-sewn, cotton, spunbond nonwoven polypropylene (NWPP), or an old sock, if it is a face mask designed to contain coughs, sneezes, and/or respiratory droplets (i.e., for source control), this guidance applies and instructions for mask cleaning and disinfection are required.

[Update 12/1/2020] The WHO updated their guidance on fabric masks with more specific information about washing masks. For details see: WHO Fabric Mask Guidance – December Updates
[Update 6/7/2020] The WHO released guidance (June 5, 2020) on fabric masks including general information about boiling and steaming fabric masks containing combinations of cotton and NWPP. Stay tuned for guidance specific updates!

Overview: A Practical Guide to Cleaning and Disinfection

Reusable fabric face masks offer many practical benefits, but it is critical to approach reuse carefully. Starting with the basics – face masks are personal: they should be worn by one user and should not be shared. Since they are designed as a barrier to droplets that may be infectious, they should be assumed dirty after every use and should be disinfected appropriately. As with any barrier, they are less effective if damaged, so masks should be inspected for defects prior to each use and discarded if defects are detected or if concerns arise.

It should go without saying, but face masks should also be kept clean — free from food residues, dirt, contamination, and other soiling. They should be washed or laundered between uses if they become sticky, visibly soiled, and/or difficult to breathe through. If heavily soiled, face masks should be discarded.

The table below provides a framework for thinking about mask cleaning and disinfection along a risk continuum. Cleaning alone carries the highest risk, disposal after a single use carries the lowest risk, and various disinfecting strategies lie in between.

Reuse Strategies for Community Masks			Advantage	Disadvantages
Highest Risk Tolerance	Cleaning Alone	Washing Hand wash with detergent; rinse thoroughly Machine wash with detergent (CDC Recommendation)	Convenience and Familiarity	High degree of variability; detergent residue may cause skin irritation; fragrances and harsh chemicals may pose inhalation risks.
	Disinfecting (with or without cleaning)	7 Days in a Paper Bag	~ 99.9% effective Minimal effort. Does not require water. Can be used for N95s and other meltblown materials that cannot be washed or boiled.	Requires more masks. Requires well controlled environment. Less effective than boiling.
		Boil (MakerMask Preferred) Boiling Alone Rinse & Boil Wash & Boil	~ 99.9999% effective Commonly accessible, high degree of consistency; familiarity	Requires attention during the 10-minute boiling time period
		Home ‘Autoclave’ (Steam Sterilize with Pressure Cooker or Instapot) Home Autoclave alone Rinse and Home Autoclave Wash & Home Autoclave	~ 100% effective (theoretically can sterilize) Reduces physical agitation of materials and may extend longevity of masks	Experimental use. Requires specialized equipment. Closer to melting point of materials. No formal evaluation for this use; unknown hazards may exist.
		Autoclave (moist heat) Clean and autoclave per facility infection control policies	~ 100% effective (theoretically can sterilize) Reduces physical agitation of materials and may extend longevity of masks. Familiar to health care facilities.	Requires specialized equipment. Not accessible to home users. Closer to melting point of materials.
No Risk Tolerance	DISCARD	Single use	Reduces risk of cross-contamination. Leaves high risk infection control to professional facilities.	Environmental impact. Limitations of source materials. Requires more masks

Figure 1. NOTE: Although these mask cleaning and disinfection recommendations are thoroughly researched and have been tested in homes and facilities around the country, they have not been evaluated by the standardized processes for approval or validation through the FDA. See Disclaimer at end of document.

Inspect Masks Prior to Each Use

It is important to note that mask materials are likely to degrade over time and with repeated washing/disinfection cycles regardless of the mask materials used. For most reusable fabric masks the exact number of cycles before mask performance degrades is still unknown. However, the WHO suggests reusable masks should be able to withstand at least 5 cleaning/disinfection cycles. Prior to each use inspect masks carefully for defects and/or damage.

For fabrics like NWPP, water-resistance is expected to diminish after repeated cleaning and/or disinfection cycles. To check the water-resistance of mask materials like spunbond nonwoven polypropylene (NWPP), a ‘flick’ test can be performed by flicking water at the surface of the mask. If the water gets absorbed by the material, it is no longer water-resistant and may be less effective as a barrier to droplets. To maximize the water resistance of mask fabrics the following steps can be taken:

Rinse fabrics thoroughly after washing as soaps and detergents are typically surfactants that reduce the water repellent properties of mask fabrics.
Avoid fabric softeners, dryer sheets, or other conditions that lubricate fabrics and leave residues that may reduce water resistance.
Reduce excess agitation while washing (e.g., wash on gentle cycles or place masks in lingerie bags while washing) and do NOT ring dry. Gentle handling while washing will increase the longevity of masks.

For more advice of cleaning masks see the section on Cleaning below. For more information on water-resistant mask materials see: The Big 4: Criteria for Community Mask Materials

Definitions: Mask Cleaning and Disinfection

In the context of infection control, cleaning and disinfection are different processes with different goals. For this discussion, we define cleaning and disinfecting based on the definitions used by the FDA (e.g., for medical washers and medical devices) as summarized below:

Cleaning refers to the physical removal of organic material or soil from objects, usually done by using water with or without detergents, manually or mechanically (AAMI, 1995). In general, the goal of cleaning is to remove microorganisms and not to kill them (Garner, 1985). In the context of reusable face masks, cleaning can be accomplished by rinsing with copious amounts of water, handwashing with detergent, or machine washing in accordance with the CDC’s recommendations for face masks, “A washing machine should suffice in properly washing a face covering.“
Disinfecting refers to the destruction of microorganisms by physical processes like heat, or by chemical means. The goal of disinfection is to kill and/or inactivate most microorganisms, but it may not kill everything (AAMI, 1995). The degree to which disinfection is successful is measured in terms of the logarithmic reduction in active pathogens (Log10 reductions), typically disinfection (i.e. pathogen inactivation) is considered successful if there is a 6 Log10 reduction in pathogens, or 99.9999% reduction, which means that only one pathogen out of every million is left.

Figure 2. Disinfectant Effectiveness on a scale of one to six where one is a 90% reduction and six is a 99.9999% reduction (image from: ‘Log Reductions – A Beginner’s Guide)

Deeper Dive: Recommendations for the degree of cleaning and disinfection required before reusing items like face masks are typically determined by which of the three Spaulding Categories it falls into based on intended use and the degree of risk to infection: critical, semi-critical, an noncritical. For noncritical devices like masks used for source control, masks may be reused after thorough cleaning and/or disinfection (FDA EUA April 24, 2014). Face masks, cloth face coverings, and fabric masks intended for use as source control are considered non-critical devices because they “are instruments and other devices whose surfaces contact only intact skin and do not penetrate it” and the “FDA recommends thorough cleaning, then intermediate or low level disinfection for non-critical devices depending on the nature and extent of contamination.” However, in home settings the CDC suggests, that noncritical items can be cleaned with a detergent and “in general, sterilization of critical items is not practical in homes but theoretically could be accomplished by … boiling.”

Mask Cleaning and Washing Advice

According to FDA reprocessing information and CDC guidance for cloth face masks, washing alone may be sufficient for fabric masks used as source control by a single individual to contain their own respiratory secretions if the mask has not been exposed to anyone else’s bodily fluids or secretions (i.e., if cross-contamination is unlikely).

Cleaning can be accomplished handwashing with detergent, or machine washing in accordance with the CDC’s recommendations for face masks, “A washing machine should suffice in properly washing a face covering.” An additional rinse cycle when cleaning a mask is recommended for all washing methods to remove any residual cleaning agents.

Detergents: detergent residue may cause skin irritation. Consider using fragrance-free, no residue detergents for masks. For more information refer to EPA Safer Choice detergents, or see recommendations from the National Eczema Association. Occasional washing with a low concentration of distilled white vinegar (e.g., ½ cup for machine washing) may help reduce build-up of detergent residues. Detergents are surfactants, and any detergent residue may reduce the water resistance of mask fabrics. Avoid detergents with conditions that may leave residue on masks.
Bleach: CAUTION, in general, bleach is NOT recommended for washing face masks as residual odors and chlorine off-gassing have been reported and could cause serious irritation or harm to the wearer. Additional information about bleach is summarized in the references section at the end.
Fabric Softener: fabric softener is NOT recommended when washing masks because it leaves a residue on mask fibers that may reduce water resistance and other technical properties of mask fabrics.

For nonwoven polypropylene (NWPP) MakerMask designs, we recommend the following washing procedures:

Note: If handling dirty laundry from a sick individual, gloves should be worn, shaking of dirty laundry should be minimized to reduce dispersal risk, and items should be laundered using the warmest appropriate water setting for the items and dried completely.
See JAMA for more information

Mask Disinfection Advice

Disinfection after each use is a best practice for all reusable masks, regardless of style or material. Although disinfection is commonly associated with the use of chemical treatments, it can also be achieved with heat (e.g., boiling or autoclaving), which is the preferred method for masks. Harsh chemicals (e.g., bleach) are not recommended as residuals of the chemicals can be trapped in the mask and may cause unintended inhalation risks or irritation.

The goal of disinfection is to kill anything that might be growing on, or inside the mask, with the goal of inactivating 6 Log10, or 99.9999% of pathogenic microorganisms. Although 6 Log10 disinfection cannot be guaranteed, it is the goal of the disinfection processes recommended by MakerMask.

For spunbond nonwoven polypropylene MakerMask designs, we recommend the following disinfection procedures:

Deeper Dive: One of the advantages of using 100% spunbond NWPP, such as that used in high-quality reusable grocery bags/conference bags, is that it is primarily homopolymer isotactic polypropylene, which has a melting point between 160 and
166 °C (320 to 331 °F) and is safe to boil (100 °C / 212 °F at sea level) or steam/autoclave at 121 °C / 250 °F. Industry guidance for decorating NWPP tote bags without melting suggests a maximum temperature of 275 °F. For more information see: https://makermask.org/the-big-four-criteria-for-community-mask-materials/

Process	Isotactic Polypropylene (NWPP Bags)
Boil	100 °C	212 °F
Iron on Low (i.e., for pressing nylon, polypropylene and spandex)	≤ 110 °C	230 °F
Autoclave (moist heat; 121 °C)	121 °C	250 °F
Autoclave (moist heat; 132 °C)	132 °C	270 °F
Max. Heat Pressing Temp for NWPP Bags	135 °C	275 °F
Iron on Medium (i.e., for pressing polyester, silk, and wool)	≤ 150°C	≤ 302 °F
NWPP tote bag melting point	160°C	331 °F
Iron on High (i.e., for pressing cotton and linen)	200°C	392 °F

Figure 3. Temperatures of common processes in relation to the melting point of isotactic nonwoven polypropylene, such as that found in reusable NWPP bags.

The Science of Disinfecting by Boiling

The science of disinfection by boiling is most simply understood in the context of boiling drinking water. Boiling is recommended by both the CDC and the WHO for disinfecting water because boiling inactivates bacteria, protozoa, and viruses in liquids (CDC Water Disinfection; WHO Guidelines for Drinking Water Quality).

For water, the WHO reports that bringing to a rolling boil, where large bubbles rise quickly to the surface of the liquid, for one minute and allowing to cool is a successful method for disinfection of water by typical users (6 Log10 reduction) as well as the most successful users (9+ Log10 reduction), see table below.

Figure 4. Effectiveness of methods for disinfecting water, adapted from WHO Guidelines for Drinking Water Quality (2017). Method used: “Bring water to a rolling boil and allow to cool.” Note: the cooling time is important as disinfection continues as long as the temperature of the water remains above 70°C (158°C).

Treatment Process	Pathogen Group	Typical User Log10 Reduction Value	Best User Log10 Reduction Value	Success for ≥6 Log10 Reduction Value
Thermal Disinfection (e.g. boiling)	Bacteria	6	9+	PASS
	Viruses	6	9+	PASS
	Protozoa	6	9+	PASS
Solar disinfection (solar UV radiation + thermal effects)	Bacteria	3	5+	FAIL
	Viruses	2	4+	FAIL
	Protozoa	2	5+	FAIL
UV light technologies using lamps	Bacteria	3	5+	FAIL
	Viruses	2	5+	FAIL
	Protozoa	3	5+	FAIL

Although short periods of boiling followed by long periods of cooling are effective for disinfection of water, disinfection can be also achieved through longer boiling times with shorter cooling periods.

Deeper Dive: Boiling and SARS-CoV. In general, studies have shown that boiling and other methods of thermal disinfection are effective for inactivating the SARS-CoV-1 viruses (Rabenau et al 2005, Lee at al 2005, Kariwa et al 2004, Geller et al 2012, as well as studies by the WHO). For SARS-CoV-1, the virus responsible for SARS, boiling for 10 minutes at 100 °C led to inactivation of the virus (Lee et al, 2005; Rabenau et al, 2005). The mechanism of inactivation was protein aggregation, which frequently results in loss of protein function. After boiling, SARS-CoV-1 was no longer detectible in western blot protein analyses.

For SARS-CoV-2, the virus responsible for COVID-19, more recent data demonstrated that heating fluid samples at 92°C (198°F) for 15 minutes was able to totally inactivate the virus in respiratory samples (Pastorino et al, 2020). Heating viral samples to boiling temperatures of 100°C (212°F) reduces the overall time required for the same level of inactivation.

For an even deeper dive into the temperature dependent inactivation of SARS-CoV-1, SARS-CoV-2, and MERS-CoV, check out the data and modeling efforts by Yan et al, 2020!

The Science of Disinfecting by Steaming

For those with access to autoclaves, MakerMask recommends autoclaving with moist heat at 121C as an alternative to boiling.

According to the CDC, “moist heat in the form of saturated steam under pressure is the most widely used and the most dependable” method for disinfecting/sterilizing things. In health care settings, autoclaving is the most common method used for steam sterilization/disinfection and the temperature, time, and pressure are all carefully controlled. These parameters may vary depending on the mask materials used and degree of disinfection required. For nonwoven polypropylene (NWPP) MakerMask designs, moist heat at 121°C is recommended, as higher temperatures may be detrimental to the NWPP. In general, the guidance for steam sterilization from the WHO is to autoclave 15 minutes at 121-124 °C (200 kPa).” In the context of NWPP masks, ECRI suggests humid heat with autoclaves or pressure cookers “requires 10 minutes at 121°C at a minimum to be effective,” for steam sterilization.

As of April 2020, the CDC suggested that based on the limited research available, moist heat (steam treatment) is one of the most promising potential methods for decontaminating nonwoven polypropylene-based masks and respirators. After thorough evaluation of the literature, and feedback from users in both home and health care settings, MakerMask recommends autoclaving at 121°C (250°F), 15 psi (1 bar) pressure for 10 minutes for disinfection/sterilization of NWPP masks.

For those interested in home autoclaving options, electronic pressure cookers (e.g. Instapot) claim to be able to provide ‘scientific-grade sterilization’ at home. These claims are supported by Swenson et al, 2018: “the pressure cookers tested are a viable alternative for steam sterilizing laboratory items when an autoclave is unavailable. In this work, only 15 mins of time in the pressure cookers was necessary to inactivate the microbes in growth media such that no growth was observed.” Although data suggests that electronic pressure cookers can be used for disinfection, the safety and efficacy of their use for NWPP masks is still considered experimental. Preliminary feedback from users exploring pressure-cooker based disinfection procedures is positive, with the most commonly cited procedure adapted from Instructables: How to Sterilize Autoclavable Materials at Home Using a Pressure Cooker.

Note: Use electronic pressure cookers in accordance with manufacturer’s instructions, read the manual. The ‘high’ setting on electronic pressure cookers typically uses a pressure of 2–11.6 psi (0.7 bar – 0.8 bar) and a temperature of 239°F-244°F (115°C – 118°C). Maximum temperatures and pressures may vary. Use at your own risk.

CAUTION: While methods are circulating for steam sterilization of masks in home microwaves, metallic nose wires present a significant fire hazard due to electrical arcing. Masks with metallic components should never be placed in a microwave.

Other Disinfection Methods

Other disinfection methods may be used in special circumstances in healthcare settings. However, these are not recommended for home use due to differences in mask materials, available equipment, the complexity of execution and/or potential for harm if not done correctly.

Inactivation by Inaction

Based on data from SARS-CoV-2 survival rates on various surfaces (van Doremalen et al., 2020; Chin et al., 2020), New York City has proposed that healthcare workers can store used N95 respirators in brown paper bags for 7 days in warm, dry environments to inactivate the virus. This method requires carefully controlled environments, and according to the limited data available is likely less effective (a 3+ log 10 reduction instead a 6+ log 10 reduction) than boiling (Chin et al, 2020). Although we recommend proper storage of masks between uses, we do not recommend inaction as a primary method of disinfection.

Deeper Dive: It is important to note that inactivation by inaction is used as a crisis alternate strategy with N95s and respirators constructed from meltblown polypropylene and/or other materials that are not suitable for washing and heat-based disinfection methods. The CDC recommends that N95s be re-used no more than 5 times, and that respirators should be left in paper bags for at least five days between uses based on the work by van Doremalen et al., 2020. MakerMask is more conservative in their advice, suggesting at least 7 days inactivation for masks based on addition information about virus survival on masks from Chin et al, 2020. For more information about potential re-use of N95s in healthcare settings, refer to the CDC’s guidance at: Implementing Filtering Facepiece Respirator (FFR) Reuse, Including Reuse after Decontamination, When There Are Known Shortages of N95 Respirators.

CAUTION: Storing masks in plastic bags instead of paper can lead to retention of residual moisture, longer virus lifetimes, and growth of mold and other harmful contaminants.

Hydrogen Peroxide and UV-C

Other possible sterilization methods being considered for use in healthcare settings include vaporized hydrogen peroxide gas plasma (FDA EUA) and UV-C irradiation (FDA risk note for use with CPAP machines). The latest data and suggested protocols for use with N95 masks are collected at https://www.n95decon.org/example-processes. It is important to note that ultraviolet irradiation methods are “unlikely to kill all the viruses and bacteria” in face masks with multiple layers, pleats, and/or seams. MakerMask does not recommend hydrogen peroxide plasma or UV-C methods for home use or by untrained individuals.

Conclusion

In summary, reusable masks should be cleaned by hand or laundered when soiled and disinfected following each use. For disinfection, MakerMask recommends boiling for 10 minutes, or autoclaving (moist heat) at 121°C (250°F), 15 psi (1 bar) pressure for 15 minutes. For those considering “inactivation by inaction” by storing masks in a brown paper bags, timelines should not be shorter than seven days.

Still have questions about mask cleaning and disinfection procedures? Join the dialogue at www.facebook.com/themakermask or www.twitter.com/themakermask.

NOTE: Although these cleaning and disinfection recommendations are thoroughly researched and have been tested in homes and facilities around the country, they have not been evaluated by the standardized processes for approval or validation through the FDA. The safety and effectiveness of the recommended procedures has not been proven and cannot be assumed. For more information about FDA required validation and reprocessing requirements see: Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling.

REFERENCES / DEEPER DIVES

Click on the sections below for additional details.

Disinfection by Boiling

Science Supporting Disinfection by Boiling (Quick Lit Review)

sars-CoV-2

15 minutes at 92C, >6-log reduction; Total inactivation of the virus (sars-CoV-2); Heat inactivation assays: Only the 92°C-15min protocol was able to inactivate totally the virus (>6 Log10 decrease)… These results were consistent with previous studies on SARS-CoV and MERS-CoV (11,12). There was no difference between clean or dirty conditions… when processing respiratory samples commonly exhibiting much higher viral loads (23), only the 92°C-15min protocol showed total inactivation”

Pastorino et al (2020). Evaluation of heating and chemical protocols for inactivating SARS-CoV-2. https://www.biorxiv.org/content/10.1101/2020.04.11.036855v1.full.pdf preprint doi: https://doi.org/10.1101/2020.04.11.036855. this version posted April 11, 2020.

“At 95°C, 3 minutes were enough to inactivate the virus in nasopharyngeal samples”… “The SARS-CoV-2 is relatively sensitive to heat inactivation in our laboratory conditions.”

Batéjat et al. (May 2020), Heat inactivation of the Severe Acute Respiratory Syndrome Coronavirus 2 https://www.biorxiv.org/content/10.1101/2020.05.01.067769v1.full

sars-CoV-1

“Heating at 100 °C for 10 min (boiling) in denaturing condition was suspected to be responsible for the failure to detect the membrane protein by WB analysis… It is failure to detect SARS-CoV membrane protein as monomers after treated with temperature over 80 °C.” – …. It has also been demonstrated that heat can inactivate the SARS-CoV (^{Rabenau et al., 2004}). The thermal aggregation of the membrane protein may be one of the reasons for this inactivation since protein aggregation often results in loss of their functions (^{Hoffner and Djian, 2002}^,^{Ishimaru et al., 2003}^,^{Lin et al., 2004}^,^{Murphy, 2002})

Lee et al (2005). Thermal aggregation of SARS-CoV membrane protein. Journal of virological methods, 129(2), 152–161. https://doi.org/10.1016/j.jviromet.2005.05.022, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7112854/

Heat treatment at 60 degrees C for at least 30 min must be used

Rabenau et al (2005). Stability and inactivation of SARS coronavirus. Med Microbiol Immunol. 2005;194(1-2):1‐6. doi:10.1007/s00430-004-0219-0; https://www.ncbi.nlm.nih.gov/pubmed/15118911

SARS-COV-1: Heat at 56°C kills the SARS coronavirus at around 10000 units per 15 min (quick reduction).

WHO: https://www.who.int/csr/sars/survival_2003_05_04/en/

Heating the virus at 56 degrees C for 5 min dramatically reduced the infectivity of the virus from 2.6 x 10(7) to 40 TCID50/ml, whereas heating the virus for 60 min or longer eliminated all infectivity.

Kariwa et al (2004). Inactivation of SARS coronavirus by means of povidone-iodine, physical conditions, and chemical reagents. Jpn J Vet Res. 2004;52(3):105‐112. https://www.ncbi.nlm.nih.gov/pubmed/15631008

The exposure of the virus to a temperature of 56 °C over 30 min reduced virus titer under an undetectable level, except if SARS-CoV is associated with proteins, such as 20% fetal calf serum (FCS), which bring a protection for the virus. In this case, the temperature needs to reach 60 °C over 30 min to bring virus titer below the detection limit.

Geller et al (2012). Human coronaviruses: insights into environmental resistance and its influence on the development of new antiseptic strategies. Viruses, 4(11), 3044–3068. https://doi.org/10.3390/v4113044, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3509683/

Viral inactivation by heat treatment at 60 degrees C required 15 to 30 minutes to inactivate the SARS-CoV.

Darnell ME, Taylor DR. Evaluation of inactivation methods for severe acute respiratory syndrome coronavirus in noncellular blood products. Transfusion. 2006;46(10):1770‐1777. doi:10.1111/j.1537-2995.2006.00976.x https://www.ncbi.nlm.nih.gov/pubmed/17002634

Water Disinfection

Boil water, if you do not have bottled water. Boiling is sufficient to kill pathogenic bacteria, viruses and protozoa (WHO, 2015). Bring water to a rolling boil for at least one minute. At altitudes above 5,000 feet (1,000 meters), boil water for three minutes.

EPA: https://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water

“Disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects… In general, sterilization of critical items is not practical in homes but theoretically could be accomplished by chemical sterilants or boiling (CDC Disinfection & Sterilization, 2019).”

CDC Disinfection & Sterilization (2019), Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008; Update: May 2019, https://www.cdc.gov/infectioncontrol/guidelines/disinfection/index.html

“Boiling is the surest method to kill disease-causing organisms, including viruses, bacteria, and parasites. Most germs die quickly at high temperatures. Water that has been boiled for 1 minute is safe to drink after it has cooled. If no other means of water treatment is available, an alternative to boiling is to use tap water that is too hot to touch, which is probably at a temperature between 131°F (55°C) and 140°F (60°C). This temperature may be adequate to kill pathogens if the water has been kept hot for some time.”

CDC: https://www.cdc.gov/healthywater/emergency/drinking/making-water-safe.html

Most germs die quickly at high temperatures. Water that has been boiled for 1 minute is safe to drink after it has cooled. If no other means of water treatment is available, an alternative to boiling is to use tap water that is too hot to touch, which is probably at a temperature between 131°F (55°C) and 140°F (60°C). This temperature may be adequate to kill pathogens if the water has been kept hot for some time.

CDC: https://wwwnc.cdc.gov/travel/page/water-disinfection

Scientific basis for the efficacy of boiling. Enteric bacteria, protozoa and viruses in liquids are sensitive to inactivation at temperatures below 100 °C. Thermal inactivation has been examined in water, sewage, milk and other liquids at temperatures close to those used for pasteurization (e.g. 63 °C for 30 minutes, 72 °C for 15 seconds) and in hot water (about 60 °C). Only a few studies have examined thermal inactivation in liquids at temperatures approaching 100 °C. The results of these investigations, which are summarized in Table 1, show that bacteria are particularly sensitive to heat, and rapid kills – less than 1 minute per log (90%) reduction – are achieved at temperatures above 65 °C. Viruses are inactivated at temperatures between 60 °C and 65 °C, but more slowly than bacteria. However, as shown for poliovirus and hepatitis A, as temperatures increase above 70 °C, a greater than 5 log inactivation (99.999% reduction) is achieved in less than 1 minute.

WHO: https://www.who.int/water_sanitation_health/dwq/Boiling_water_01_15.pdf

“Bringing water to a rolling boil is the simplest and most effective way to kill all disease-causing pathogens, even in turbid water and at high altitudes (WHO Guidelines for Drinking Water Quality).”… “Boiling: Bring water to a rolling boil and allow to cool; Kills all pathogens” …. Thermal (heat) technologies: Thermal technologies are those whose primary mechanism for the destruction of microbes in water is heat produced by burning fuel. These include boiling and heating to pasteurization temperatures (typically > 63 °C for 30 minutes when applied to milk). The recommended procedure for water treatment is to raise the temperature so that a rolling boil is achieved, removing the water from the heat and allowing it to cool naturally, and then protecting it from post-treatment contamination during storage (see the supporting document Boil water; Annex 1). The above-mentioned solar technologies using solar radiation for heat or for a combination of heat and UV radiation from sunlight are distinguished from this category.”

WHO Guidelines for Drinking Water Quality (2017). Guidelines for drinking-water quality, 4th edition, incorporating the 1st addendum (2017), https://apps.who.int/iris/bitstream/handle/10665/254637/9789241549950-eng.pdf;jsessionid=C2EB6D1DD33B342DF9798E2BE078D195?sequence=1
WHO Inactivation https://www.who.int/water_sanitation_health/water-quality/guidelines/en/watreatpath3.pdf?ua=1

Home Disinfection

What is the best way to sterilize a cleaning cloth? (http://www.dranniesexperiments.com/cleaning-cloth-testing/what-is-the-best-way-to-sterilize-a-cleaning-cloth#TOC-BOILING)

Disinfection by Steam

Science Supporting Disinfection by Steam (Quick Lit Review)

Steam Sterilization

According to the CDC, “Of all the methods available for sterilization, moist heat in the form of saturated steam under pressure is the most widely used and the most dependable. Steam sterilization is nontoxic, inexpensive, rapidly microbicidal, sporicidal, and rapidly heats and penetrates fabrics… Mode of Action. Moist heat destroys microorganisms by the irreversible coagulation and denaturation of enzymes and structural proteins. In support of this fact, it has been found that the presence of moisture significantly affects the coagulation temperature of proteins and the temperature at which microorganisms are destroyed.” https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfection-guidelines-H.pdf

According to ECRI, in the context of masks, “Steam sterilization requires 10 minutes at 121°C at a minimum to be effective.” – https://www.elsevier.com/__data/assets/pdf_file/0006/997863/COVID-ECRI-N95-Respirators_2020-03.pdf

According to the WHO, “The recommendations for sterilization in an autoclave are 15 minutes at 121-124 °C (200 kPa).” https://apps.who.int/phint/pdf/b/7.5.9.5.8-Methods-of-sterilization.pdf

Pressure Cookers as Autoclaves

Instapot. Who knew that Instant Pot can provide scientific-grade sterilization? https://instantpot.com/who-knew-that-instant-pot-can-provides-scientific-grade-sterilization-actually-we-did/

Assessment and verification of commercially available pressure cookers for laboratory sterilization. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0208769

Using a pressure cooker as an autoclave. EPI Newsl. 1984;6(6):5‐8. https://pubmed.ncbi.nlm.nih.gov/12267939/

How to Sterilize Autoclavable Materials at Home Using a Pressure Cooker. https://www.instructables.com/id/How-to-Sterilize-Autoclavable-Materials-at-Home-us/

Can You Use a Pressure Cooker as an Autoclave? Science Says Sure, in Some Situations. https://microbialmenagerie.com/can-you-use-a-pressure-cooker-as-an-autoclave-science-says-sure-in-some-situations/ “Steam heating to 121°C at 15 PSI for ~20 minutes per liter of liquid is standard practice to consider something sterile.”

Using Commercial Pressure Cookers to Sterilize Dental Instruments in Remote Settings, https://azahec.uahs.arizona.edu/sites/default/files/u132/19-arnett_rhpp_pressure_cooker.pdf

Masks & Steam

“Disinfection of used masks is needed for reuse of them with safety, but improper decontamination can damage the blocking structure of masks. In this study, we demonstrated, using avian coronavirus of infectious bronchitis virus to mimic SARS-CoV-2, that medical masks and N95 masks remained their blocking efficacy after being steamed on boiling water even for 2 hours.” https://www.ncbi.nlm.nih.gov/pubmed/32320083

https://www.journalofhospitalinfection.com/article/S0195-6701(20)30176-6/fulltext

NWPP Autoclave

Polypropylene

“Steam sterilization is generally carried out at temperatures between 121°C (250°F) and 134°C (273°F), under 15 psi (0.5 bar) pressure, between 10 and 60 min, depending upon the material and need. Most plastics will survive 1–5 cycles of steam sterilization.” (Material Requirements for Plastics Used in Medical Devices. Vinny R. Sastri, in Plastics in Medical Devices (Second Edition), 2014. https://www.sciencedirect.com/topics/engineering/steam-sterilization)

Autoclaving Capability and Heat Distortion Temperatures of Plastics Used in Medical Applications

PP*	100–120	Good	Fair	Good
PP copolymers	85–105	Good	Fair	Good

“Polypropylene is an inexpensive resin that can resist autoclave temperatures.”

https://ehs.princeton.edu/book/export/html/380

Polypropylene is compatible with steam sterilization at 121°C, Foster Company, “ https://www.fostercomp.com/wp-content/uploads/2018/12/Presentation-Content-Sterilization-of-Medical-Devices.pdf

Reprocessing and Laundering

Cleaning / Laundry
Reprocessing / Laundry	“The antimicrobial action of the laundering process results from a combination of mechanical, thermal, and chemical factors. Dilution and agitation in water remove substantial quantities of microorganisms. Soaps and detergentsfunction to suspend soils and also exhibit some microbiocidal properties. Hot water provides an effective means of destroying microorganisms. A temperature of at least 160°F (71°C) for a minimum of 25 minutes is commonly recommended for hot-water washing. Water of this temperature can be provided by steam jet or separate booster heater. The use of chlorine bleach assures an extra margin of safety. A total available chlorine residual of 50–150 ppm is usually achieved during the bleach cycle. Chlorine bleach becomes activated at water temperatures of 135°F–145°F (57.2°C–62.7°C). The last of the series of rinse cycles is the addition of a mild acid (i.e., sour) to neutralize any alkalinity in the water supply, soap, or detergent. The rapid shift in pH from approximately 12 to 5 is an effective means to inactivate some microorganisms. Effective removal of residual alkali from fabrics is an important measure in reducing the risk for skin reactions among patients.” – https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/laundry.html “Fabrics, textiles, and clothing used in health-care settings are disinfected during laundering and generally rendered free of vegetative pathogens (i.e., hygienically clean), but they are not sterile. Laundering cycles consist of flush, main wash, bleaching, rinsing, and souring.” – https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/laundry.html
	“Yes. Cloth gowns that will not be used in a sterile field, such as surgery, can be reused if they are laundered in enzymatic detergent or per the hospital’s SOP” – https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/faqs-shortages-surgical-masks-and-gowns-during-covid-19-pandemic
	FDA – Reprocessing of Reusable Medical Devices: Information for Manufacturers -2018 FDA- Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling – 2017 ). https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/questions-about-personal-protective-equipment-ppe Guidance Document For Washers And Washer-Disinfectors Intended For Processing Reusable Medical Devices, https://www.fda.gov/regulatory-information/search-fda-guidance-documents/guidance-document-washers-and-washer-disinfectors-intended-processing-reusable-medical-devices Frequently Asked Questions on Soap. https://www.fda.gov/cosmetics/cosmetic-products/frequently-asked-questions-soap CDC Laundry for Infection Control: https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/laundry.html, OSHA regulations prohibit home laundering of items that are considered personal protective apparel or equipment (e.g., laboratory coats) The CDC provides general procedures for cleaning face masks and cloth face coverings (see https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth-face-coverings.html), and specifically states: “A washing machine should suffice in properly washing a face covering.” “They should be routinely washed depending on the frequency of use” And for food workers clarifies (see https://www.fda.gov/food/food-safety-during-emergencies/use-respirators-facemasks-and-cloth-face-coverings-food-and-agriculture-sector-during-coronavirus): Launder reusable face coverings before each daily use. Maintain face coverings in accordance with parameters in FDA’s Model Food Code sections 4-801.11 Clean Linens and 4.802.11 Specifications, as applicable. After low level disinfection (typically effective against vegetative forms of bacteria, some fungi, and lipid viruses) After intermediate level disinfection (typically effective against viruses, mycobacteria, fungi, and vegetative bacteria, but not bacterial spores when used according to labeling) NOTE: “An effective FFR decontamination method should reduce the pathogen burden, maintain the function of the FFR, and present no residual chemical hazard…. Ultraviolet germicidal irradiation (UVGI), vaporous hydrogen peroxide (VHP), and moist heat showed the most promise as potential methods to decontaminate FFRs. Therefore, researchers, decontamination companies, healthcare systems, or individual hospitals should focus current efforts on these technologies.” –https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html
Industry Advice	“You must not use aromatic-based solutions or scented oils (e.g., eucalyptus or essential oils), bleach, alcohol or products that smell strongly (e.g., citrus) to clean any of the mask components. Some cleaning products could damage the mask, its parts and their function, or leave harmful residual vapours that could be inhaled if not rinsed thoroughly.” … “You should always follow the cleaning instructions in your mask user guide and use mild soap. We recommend using ordinary washing up liquid or baby shampoo to wash your mask” https://www.resmed.com/epn/en/consumer/support/masks/how-to-clean-your-mask.html
Bleach	OSHA Respirator Cleaning: “Hypochlorite solution (50 ppm of chlorine) made by adding approximately one milliliter of laundry bleach to one liter of water at 43 deg. C (110 deg. F); Rinse components thoroughly in clean, warm (43 deg. C [110 deg. F] maximum), preferably running water. Drain. The importance of thorough rinsing cannot be overemphasized. Detergents or disinfectants that dry on facepieces may result in dermatitis. In addition, some disinfectants may cause deterioration of rubber or corrosion of metal parts if not completely removed.” https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.134AppB2 Bleach Product Label: 1 tbsp Clorox Bleach in 1 gallon of water == 200 ppm chlorine, concentration recommended for laundering https://www3.epa.gov/pesticides/chem_search/ppls/005813-00001-20110913.pdf Bleach Hazardous Substance Fact Sheet; NIOSH: The recommended airborne exposure limit (REL) is 0.5 ppm (as Chlorine), which should not be exceeded during any 15-minute work period. AIHA: The American Industrial Hygiene Association recommends a Workplace Environmental Exposure Level (WEEL) of 2 mg/m3 for a 15-minute work period. https://nj.gov/health/eoh/rtkweb/documents/fs/1707.pdf https://www.cdc.gov/niosh/idlh/7782505.html “In fact, the odor threshold for chlorine (when the scent is noticeable) is listed at 0.002 ppm in air and 0.31 ppm in water (EPA 1994b, 1999). Perceivable sensory irritation, however, occurs at 1.0 ppm in air, 500 times that of the odor threshold (EPA 1999. Cited from Toxicology Profile for Chlorine, ASTDR, USDHHS, September 2007). Odor complaints for bleach are not unlike complaints received for any other chemical with a noticeable smell. Investigation by Paustenbauch and Gaffney (Intl. Occup Env. Health. 79: 339-342, 2006) found that for some odorous chemicals, even when one maintains airborne concentrations below a particular OEL (Occupational Exposure Limit), this level of exposure may not be adequate to prevent all persons from reporting an appreciable adverse response.” https://www.infectioncontroltoday.com/environmental-hygiene/dispelling-myths-about-bleach-odors Bleach Inhalation (2020 Poison Control Calls) The daily number of calls to poison centers increased sharply at the beginning of March 2020 for exposures to both cleaners and disinfectants (Figure). The increase in total calls was seen across all age groups; however, exposures among children aged ≤5 years consistently represented a large percentage of total calls in the 3-month study period for each year (range = 39.9%–47.3%) (Table). Further analysis of the increase in calls from 2019 to 2020 (3,137 for cleaners, 4,591 for disinfectants), showed that among all cleaner categories, bleaches accounted for the largest percentage of the increase (1,949; 62.1%), whereas nonalcohol disinfectants (1,684; 36.7%) and hand sanitizers (1,684; 36.7%) accounted for the largest percentages of the increase among disinfectant categories. Inhalation represented the largest percentage increase from 2019 to 2020 among all exposure routes, with an increase of 35.3% (from 4,713 to 6,379) for all cleaners and an increase of 108.8% (from 569 to 1,188) for all disinfectants. “Bleach has many uses in your laundry program, your patient care setting, and your overall disinfection process. When used properly per the directions on the label, bleach is effective and safe. Regrettably, the high likelihood of misuse and improper training leaves bleach as the least safe option where other alternatives will work as effectively and have a lower likelihood of danger to people or damage to facilities. Due to the off-label use and wide variety of bleach options for sale with differing dilutions, many cleaning guidelines, including the Delaware Administrative Code, have been adjusted to remove bleach as an acceptable disinfecting solution.” – https://www.actioncleanup.com/blog-4/bleach-fumes-clean-and-healthy-or-danger-stay-away Bleach Disinfection: https://www.cdc.gov/vhf/ebola/clinicians/non-us-healthcare-settings/chlorine-use.html
Detergents	‘Fragrance – Free’ detergents, which according to the EPA means, “Fragrance-free means that fragrance materials or masking scents are not used in the product.” https://www.epa.gov/sites/production/files/2016-10/documents/saferchoice-factsheet-fragrancefree_0.pdf More Info: https://www.mcgill.ca/oss/article/quirky-science-you-asked/what-difference-between-unscented-and-fragrance-free-products ‘Fragrance – Free’ that meet Safer Choice Standards 23 Dish Soaps Listed as ‘Fragrance- Free’ and meet the EPA Safer Choice Standards https://www.epa.gov/saferchoice/products#type=Dish%20Soaps 47 Laundry Detergents Soaps Listed as ‘Fragrance- Free’ and meet the EPA Safer Choice Standards. https://www.epa.gov/saferchoice/products#search=Laundry%20Products%20: Dermatologist recommended detergents: https://nationaleczema.org/laundry-care-for-people-eczema/ https://nationaleczema.org/eczema-products/?fwp_product_category=household-products NEA Seal of Acceptance: All Free and Clear Liquid Laundry Detergent All Free and Clear Mighty Pacs Laundry Detergent Attitude Sensitive Skin Baby Laundry Detergent Attitude Sensitive Skin Baby Bottle and Dishwashing Foam Attitude Sensitive Skin Dishwashing Liquid Tide Free and Gentle Liquid Laundry Detergent Honest Laundry Free and Clear Honest Baby Laundry Free and Clear National Psoriasis Foundation Seal of Recognition; https://www.psoriasis.org/seal/product-directory/household-items Tide Free and Gentle Liquid Laundry Detergent https://www.happi.com/contents/view_online-exclusives/2017-04-16/a-laundry-list-of-allergens/ FDA: Soap: https://www.fda.gov/cosmetics/cosmetic-products/frequently-asked-questions-soap Regulated by: If your product meets the regulatory definition of soap, it’s regulated by the Consumer Product Safety Commission (CPSC), not by FDA. Please direct questions about requirements for these products to CPSC. If the product contains synthetic detergents, it’s a cosmetic, not a soap. FDA Cleaning: Detergent: a. Detergent. If a detergent or soap is used for cleaning, determine and consider the difficulty that may arise when attempting to test for residues. A common problem associated with detergent use is its composition. Many detergent suppliers will not provide specific composition, which makes it difficult for the user to evaluate residues. As with product residues, it is important and it is expected that the manufacturer evaluate the efficiency of the cleaning process for the removal of residues. However, unlike product residues, it is expected that no (or for ultra sensitive analytical test methods – very low) detergent levels remain after cleaning. Detergents are not part of the manufacturing process and are only added to facilitate cleaning during the cleaning process. Thus, they should be easily removable. Otherwise, a different detergent should be selected. –https://www.fda.gov/validation-cleaning-processes-793 “ What are the effects of laundry residue on humans? An increasing slice of the population is experiencing episodes of eczema, psoriasis, and other reactive skin irritations loosely referred to as contact dermatitis. In cases where the irritation clearly stops where clothing contact stops, most pediatricians, dermatologists, and allergists will recommend elimination of fabric softener.” – http://www.atsko.com/the-detergent-conspiracy/ https://news.wisc.edu/curiosities-whats-the-difference-between-dishwasher-detergent-laundry-detergent-and-dish-soap-why-arent-they-interchangeable/
Disinfectants	420 EPA Registered Disinfectancts for SARS-CoV-2 https://www.epa.gov/sites/production/files/2020-04/documents/316485-b_reopeningamerica_combo_placard_infographic_4.19_6pm.pdf https://www.epa.gov/sites/production/files/2020-04/documents/316485-c_reopeningamerica_guidance_4.19_6pm.pdf

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