We propose a general mechanism behind the UV protective properties. We provided additional empirical confirmation of the previously proposed 'molecular sunscreen' mechanism by performing the experiment where two quartz cuvettes were stacked one after another (Figure ). Only mixing virions with BB allowed for protection. We found that the common feature for the dyes that protected phages (including Congo red) was the presence of negatively charged sulfonic groups (SO3 -). Crystal violet, a triarylmethane dye of a similar molecular structure and UV-Vis spectrum to BB, protected neither bacteriophages (Figure ) nor bacteria from UV exposure (Figure ).