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With the rise and spread of the new coronavirus (COVID-19) epidemic situation, all the masks are out of stock, or they are really hard to find. You may wonder if you can disinfect and reuse disposable masks. How to disinfect the mask without destroying its protective function?

Let's talk about protective function of the masks.
At present, it is believed that both N95 mask and medical surgical mask can effectively protect the user from the new coronavirus if using them correctly. Structurally, the filter layer of these masks (N95 and medical surgical mask) is made of non-woven fiber material, which can make tiny particles adhere to its fiber. Breathing air is not obstructed and can easily pass through the filter material. The mechanism of filtration is mainly inertial collision, diffusion and electrostatic adsorption. The premise of using the mask again after disinfection is that the sterilized mask can neither affect the free circulation of air nor destroy the filtering mechanism of the mask. So, what kind of disinfection can meet these two points?

 

To find out the influence on the filtration mechanism of masks (N95 mask and medical surgical mask), five disinfection methods were compared: 1) oven dry heat disinfection, 2) alcohol spraying disinfection, 3) steamer wet heat disinfection, 4) high temperature and high-pressure disinfection and 5) ultraviolet disinfection.

1. It was found that dry heat disinfection (heating at 70 ℃ for 30 minutes) had the least effect on damaging the filtering mechanism, and the filtering effect could be maintained above 95%.
2. The disinfection method of spraying alcohol on the mask will destroy the electrostatic absorption of the mask, causing filtering efficiency of the mask lowering below 95%.
3. Other methods such as steamer damp heat method and high-pressure high temperature sterilization methods also made the filtering efficiency of the mask lower than 95%.In addition, high temperature and high-pressure method makes the mask seriously deformed.
4. The new coronavirus is sensitive to ultraviolet rays, and ultraviolet disinfection does not affect the filtration efficiency of respirators. However, the inactivation effect of viruses in mask fibers, which cannot be directly observed, is unknown. Therefore, it is not recommended.

The new coronavirus is sensitive to heat. It can effectively inactivate the new coronavirus by heating for 30 minutes at 56 degrees Celsius. Therefore, the single dry heat sterilization (70 degrees Celsius heating for 30 minutes) can effectively inactivate the virus without affecting the protective function of the mask. However, it is uncertain whether several times of disinfection affects the protective effect of the mask.
On February 9^th 2020, Fudan University Shanghai Medical College, Ministry of Education / Medical Molecular Virology Laboratory of Health Committee and School of Public Health together published a scientific research paper "Experimental research on safe and rapid regeneration of disposable medical masks". It was published in the Journal of Microbiology and Infection online version. The research paper confirmed that disposable medical masks could be disinfected by using following method: After using the mask, it can be wrapped with household fresh-keeping bags and treated with household electric hair dryer for 30 minutes. After that it can be used again. This method doesn’t affect masks original filter retention effect, and the contaminated viruses are inactivated! 

Cotton mask may be the only choice for some people. Because there is no such filter structure, cotton mask has a weak function of filtering virus. However, in the absence of better masks, it’s better than nothing - it can still block the droplets of the wearer. Usually cotton mask with more than 12 layers of yarn is required. It can be disinfected repeatedly. 

 

If there are not enough N95 or surgical masks, as long as the mask is not obviously contaminated, soiled or damaged, it can also be considered to be reused in a short period of time. After use you can fold the inner layer of the mask in half, hang it separately or place it in a separate packaging bag. Healthy people can use N95 mask for 8 hours continuously or intermittently, and surgical mask for 4 hours at a time. Patients with chronic respiratory diseases are not recommended to wear them for a long time.

 

Sources: 

- Discussion on the feasibility of sterilization and reuse of disposable dust mask by Yu Taishan, He Yufang, et al. Labor safety and health research quarterly 0106 (2008) 

- Pneumonia diagnosis and treatment plan for new coronavirus infection (trial version fourth) 

- Experimental study on safe and rapid regeneration of disposable medical masks, scientific research paper of Fudan University Shanghai Medical College, Ministry of education / Medical Molecular Virology Laboratory of Health Committee and School of public health