With mask shortages during the coronavirus outbreak, some doctors are sanitizing masks with alcohol so they can re-use them. But this raises questions about whether alcohol actually works and whether it degrades the masks.
Does Alcohol Kill Viruses?
The research on alcohol is clear. Alcohol kills viruses. Technically, viruses aren’t alive, so scientists focus on whether the virus is “deactivated” or no longer able to infect humans.
For example, a 2018 article summarized 17 studies where scientists put alcohol on people’s hands and measured the reduction in virus. Alcohol deactivated over 90% of viruses like the polio virus in most cases, depending on the dose and the particular virus.
However, in 23% of the trials, the alcohol deactivated less than 90% of the virus. Thus, alcohol does “kill” viruses, but not all of them all of the time.
Does Sanitizing Masks with Alcohol Degrade Masks?
But before doctors can start spraying masks with alcohol, we need to know whether the alcohol degrades the masks. Even a “successful” disinfection is useless if it harms the mask.
Fortunately, scientists have tested this question already. Researchers at the National Institute for Occupational Safety and Health tested N95 masks before and after dipping them in rubbing alcohol (isopropanol). Then they dried the masks overnight.
After the alcohol disinfection, the masks captured 37% less particulate on average.
Why This Mask Test Overstates The Effect
A 37% drop sounds big, but to be fair, this number exaggerates the overall harm. That’s because they tested the particle sizes that are the most likely to be affected by alcohol treatment.
The researchers tested particles from around 0.05 to 0.40 microns. For comparison, the coronavirus averages 0.125 microns. Of course, many particles in the air are larger than 0.4 microns, including some bacteria and even some viruses.
Why does this size range matter? This range around 0.3 microns is the hardest for masks to capture. This chart shows particle capture rates dipping around 0.3 microns. This chart is for HEPA filters, but masks follow the same pattern, with some small differences.
That’s bad news for particles in this size range, but it also means that alcohol does less harm for capturing particles outside this critical range. For example, when the researchers measured even smaller particles, they found out alcohol sterilization harmed performance by less than 5%.
Read more: Bouncing explains why it’s actually easier for masks to capture smaller particles.
Better Options Than Sanitizing Masks With Alcohol
This finding is similar to results of washing masks with soap and water, which also harms performance. Instead, research is pointing to UV light and simply drying and waiting as better options for disinfecting masks.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.