What Builds Up on an Unwashed Brush
Makeup brushes are warm, porous, and pressed against skin daily. Within 48 hours of first use, the bristle base, the dense area near the ferrule where product compacts, begins collecting dead skin cells, sebum, and residual pigment. By the end of the first week, studies from the British Journal of Ophthalmology and dermatological research on cosmetic tool contamination have documented the presence of Staphylococcus aureus, E. coli, and Aspergillus species on unwashed applicators. You do not need a lab to see the result: a foundation brush used daily for two weeks will transfer a visible grey-brown residue onto a white tissue even after the product appears gone.
