A disposable surgical mask washed up to 10 times is at least as effective as a cloth mask, according to a fresh study by the Technical Research Centre of Finland VTT which looked at cleaning of protective face masks under normal home conditions.
Among the findings was that cloth masks are best cleaned at home by boiling for at least five minutes. Machine washing at 60 degrees Celsius was the second best way to clean cloth masks for reuse.
Disposal masks can withstand up to ten washes by boiling or in a washing machine, the study says.
However, washing degrades the small particle filtering capacity of disposable masks. It is not recommended that masks intended for use in a professional setting be home washed for reuse.
"In this study, aimed at reducing mask waste, we combined VTT's expertise in materials technology and microbiology," research professor Arl Harlin states in a press release published on Friday. "We were surprised that disposable surgical face masks cleaned up to ten times are at least as effective as a fabric mask."
Surgical masks with a CE marking indicate that they have been assessed and deemed to meet EU safety, health and environmental protection requirements.
No: Oven, steaming, sunlight
Heat treatment in an oven is a promising option provided the oven temperature is close to 100 degrees Celsius. On the other hand, it is a risk to the structural integrity of the masks.
Steam cleaners cannot reliably eliminate viruses, and ironing at a high enough temperature to kill viruses clinging to the fabric, in turn, damages the permeability of the mask, making it more difficult for the user to breathe.
Sunlight is of no use in sterilising masks, at least not in Finland in the autumn. In Spain, for example, it has been recommended that a dry, sunny spot be used for long-term storage of masks, but this is not practical in the Nordic region right now.
Masks should not be microwaved because of their metal parts.
Potentially effective UV-C ultraviolet radiation treatment was not included in the VTT, although devices using this technique are coming to market.
The European Centre for Disease Prevention and Control (ECDC) has published a document on the cleaning and reuse of masks during the COVID-19 pandemic. The VTT study was carried out in response to a ECDC request to examine the methods suggested in that guide.
Recommendations and instructions for use of masks are available from the Finnish Institute for Health and Welfare (THL).