A mascara applicator comes very near the wet surface of the eye on a daily basis while also picking up whatever bacteria or other irritants may be in the other. The tendency of many buyers is to use a mascara until it runs dry. Eye doctors are urging users to discard the container within a few months, but in no event later than when it changes develops lumps, gets drier or thinner, or otherwise shows evidence of use.
Doctors and the makers of beauty products often urge disposal within a fixed and short period after they’re opened, nominally for health reasons. Skeptics may feel that the maker’s motivation is at least as much to be able to sell more product. But, particularly with mascara, the health risks are real.
And here’s an article recommending a drugstore brand of mascara that’s a relatively reasonable $10 a package: