To the naked eye, it looks pretty gross. But as several commenters pointed out, the growth here could be far worse. (Especially because the user admitted to not using the mascara very often.) According to Dr. Shereene Idriss , MD, a derm at Union Square Laser Dermatology in NYC, bacteria growth in mascara is common because of your lashes. “The main purpose [of lashes] is to protect your eyes by trapping bacteria and pollutants that can get into them,” she says. “Therefore, when you apply mascara, you are basically picking up that bacteria and introducing it into the tube of product.”