A Japanese study published in the scientific journal Nature has highlighted the hygiene issues associated with re-using face masks. The study, ‘Bacterial and fungal isolation from face masks under the Covid-19 pandemic’, found bacterial and fungal colonies on the face masks worn by 109 volunteers, including on the inner side of the masks.
The research prompted the scientists behind the study to warn those with compromised immune systems to avoid re-using face masks due to the possible growth of harmful germs.
The seven scientists from the Department of Microbiology at Kindai University and the Faculty of Medicine at Ohnohigashi, in Osakasayama, Osaka, Japan, acknowledged that while there have been extensive studies relating to the effectiveness of face masks against vital transmission, there have been few reports on the potential hygiene issues due to bacteria and fungi attached to face masks.
Researchers surveyed a total of 109 volunteers, asking them about their mask usage and lifestyles, and cultured bacteria and fungi from either the face-side or outer-side of their face masks.
Highlighting the implications for hygiene, the researchers, in the study published in July, point out that non-woven masks can end up being worn for days on end when they are supposed to be disposed of:
“Although the effectiveness of face masks against viral transmission has been extensively studied, the hygiene issues in mask usage remain unclear. The standard mask usage is disposable non-woven masks.
“In some cases, however, people may use non-woven masks repeatedly or use different types of masks in different situations depending on their socioeconomic cultures. For example, in Japan, the short supply of non-woven masks led to the repeated use of disposable non-woven masks and the use of other types of face masks, such as handmade masks and polyurethane masks. Even after the shortage of mask supply has been resolved, some people have used disposable non-woven masks repeatedly or other types of face masks”.
“Since masks can be a direct source of infection to the respiratory tract, digestive tract, and skin, it is crucial to maintain their hygiene to prevent bacterial and fungal infections that can exacerbate COVID-19”, they added.
Firstly, researchers aimed to quantify and identify the bacteria and fungi attached to face masks, and secondly, to investigate whether the mask-attached microbes could be associated with the types and usage of the masks and individual lifestyles.
They asked the survey participants about the mask type and how long they tended to wear their masks. The study noted three main types of masks that were commonly available in Japan: non-woven, polyurethane, and gauze or cloth masks.
The researchers note that although the numbers of COVID-19 patients were “relatively low” in Japan during the study period, “most people” wore face masks in public places. All of those who participated in the study wore face masks in public places. 63 males and 46 females took part in the survey, the majority of whom (78%) used non-woven face masks. The majority of those who participated wore polyurethane masks except for a few gauze or cloth mask users.
75% of those surveyed who wore non-woven masks wore the masks for a single day, while 58% of the other mask type users wore the same masks for two days or more.
“This could be because other mask types, including polyurethane, gauze, and cloth masks, are designed washable for repeated usage; the users commonly washed and reused their masks multiple times. On the other hand, we found no significant differences between genders regarding the mask types and usage duration,” researchers said.
Microbes on the masks were cultured by pressing the face-side and outer-side of the masks onto agar plates (two plates per participant: the face-side and outer-side). The agar plates were then incubated 18 hours and 5 days for bacterial and fungal propagation, respectively, and conducted colony counting.
In their findings, the researchers reported:
“The bacterial colony numbers were greater on the face-side than the outer-side; the fungal colony numbers were fewer on the face-side than the outer-side”.
Researchers found that a longer mask usage significantly increased the fungal colony numbers but not the bacterial colony numbers. Although most identified microbes were non-pathogenic in humans; Staphylococcus epidermidis, Staphylococcus aureus, and Cladosporium, we found several pathogenic microbes; Bacillus cereus, Staphylococcus saprophyticus, Aspergillus, and Microsporum.
“We also found no associations of mask-attached microbes with the transportation methods or gargling. We propose that immunocompromised people should avoid repeated use of masks to prevent microbial infection,” they said.
The researchers also noted that longer duration of mask usage correlated with increases in the fungal colony counts but not the bacterial colony counts. They also found that non-woven masks had fewer fungi than other mask types on the outer-side. Although the bacterial colony counts were comparable in all mask types, those on the face-side were lower in females than in males.
Limitations to the study included a small sample size along with the fact that not all mask types were studied, nor were factors including mask thickness and fabric coating that may impact microbial growth.