Suitability of Rose Bengal sodium salt staining for visualisation of face mask contamination by living organisms

Unworn masks and masks provided to us after having been worn conformable to law (mandatory wearing of masks) served as test objects. In order to identify the distribution of living microorganisms on the surface of a mask dependent on exposure time and distance from the human face we conducted a staining study using the bengal rose method. The regular deposition of living microorganisms on artificial mask surfaces was more intense in the areas close to the mouth and nose. A time dependent accumulation was larger on the inside in comparison to the outside of the mask, even if the mask was not worn but only left in the room. The most interesting finding was the ability of microorganisms to penetrate all layers of the mask. We therefore conclude that masks are a suitable substrate for the cultivation of germs, even when not worn. Colonisation increases with human use and with time.