Face masks: always a healthy choice during this COVID-19 pandemic?

Due to the corona pandemic, Belgium went into lockdown starting from the 18th of March 2020. Multiple changes in our day-to-day life had to be made as more and more regulations came into place. Physical distancing and wearing face masks are the ‘new normal’ in our country at the moment. Moreover, face masks are increasingly obliged in the community, outside hospitals and care facilities, mainly based on the precautionary principle, since conclusive evidence is not (yet) available. Face masks are a medical device and placebo-controlled conclusive well-controlled clinical trials that prove the benefit of wearing a face mask in community settings are lacking (Martin, 2020). Such studies are important to double check safety and efficacy of medical devices and drugs. While well-designed face masks show high efficacy in specific settings, such as in hospitals with a high chance of COVID-19 patients, they could also have some unexpected side effects. Due to a shortage of the surgical face masks at the beginning of the crisis, self-made cotton face masks are promoted, but their safety and efficacy is not well documented. Wearing them for longer periods of time, like in schools and restaurants, could result in a concentration of microbes on the masks that should be carefully monitored.

What we as bioscience engineers learn in our first microbiology lesson is that bacteria and fungi need a surface or substrate, moisture, a little bit of food, nice temperature, and an absent immune system to grow exponentially. This environment seems to be exactly what is created when wearing a face masks for multiple hours. When these masks are then not washed or disinfected properly, these bacteria might resume on the face mask even before using it.

For a scientist, “measuring is knowing” is the most important life motto and so we started experiments in the lab to determine how many bacteria could concentrate on different mask types after wearing them for four hours and how to clean them in the best way. In the figure below you can see the set-up of our experiments.

First of all, we could see that cotton masks concentrate 10 to 20 times more bacteria than the surgical-type masks tested. This might be due to the higher amount of moisture in the cotton masks and less antimicrobial and more growth supporting properties of the material used. Surgical face masks always contain a filter and consist of more absorbing material.

Furthermore, we isolated bacteria from the mouth masks and tested their resistance to the antibiotics erythromycin and ampicillin. In the figure below, you can see that almost 50% of the isolates tested were resistant to at least one antibiotic and some isolates were even resistant to both antibiotics. It has been stated by the WHO that by 2050 more people will die from an infection caused by antibiotic resistant bacteria than cancer (WHO, 2019). An important concern is that the increased use of face masks in the community should not negatively contribute to this trend. Antibiotic stewardship is still crucial, also during the COVID-19 crisis (Hsu, 2020).

Lastly, we tested different washing and disinfection methods for the self-made cotton masks, to determine the best way to get rid of these bacterial cells on the masks. We tested: washing at 100°C, washing at 60°C with soap, ironing with a steam iron, putting it in the freezer overnight and leaving it on a counter top for 72h. As can be seen in the figure below, we can recommend to either wash your mask at 100°C or 60°C with soap or use a steam iron. These methods resulted in 25 times, 60 times, and 95 times less bacteria, respectively.

Based on these results, we are no advocates for the obligation of face masks in the community at places where physical distancing is possible. A high number of bacteria is present on these masks, especially on the cotton masks, and not handling or washing them properly might be harmful. By touching the mask, bacteria and viruses present on the face mask could spread easily, especially when the masks have become humid, because liquid is known to promote microbial transfer. In addition, people that wear a face mask often touch their face more frequently, increasing the chances to spread unwanted microbes. The good news is, that the bacteria we could identify on the masks are unlikely to make you instantly sick. However, they could cause acne and other skin infections, especially in combination with the friction of the face mask on the skin. Furthermore, food infections might occur due to touching the mask with your hands. In the worst-case scenarios, lung and systemic infections can be caused since bacteria could grow exponentially out of the control of our immune system and microbiota. Especially when bacteria show antibiotic resistance, safety measures must be taken when using these masks.

As bacteriologists, we recommend to ensure social distancing and wash your hands as much as needed. These actions are very effective and should always be taken as first safety measures in the community during a pandemic. When physical distancing is not possible for longer than a few minutes (15 minutes is often used as a general rule to determine high-risk contacts) and when the SARS-CoV-2 infection rate in the community is still high, face masks are advised. But they must be used properly and stored in a breathable container to transport home or when not used for a certain period (anyway, wearing masks longer than 4 hours seems not advisable based on our results☺). If available, surgical-like masks are preferred, as they hold less bacteria, and can be easily disposed of after wearing.