According to a recently published study in the International Journal of Cosmetic Science, Brazilian researchers found staph bacteria contaminating 79 percent of 40 mascara samples women gave them for testing.
Contaminated mascara puts the user at risk for pink eye (conjunctivitis) and other inflammatory conditions, according to Women’s Health magazine, which reported on the study. The moist, dark conditions inside a mascara tube are an ideal environment for bacteria growth, and this is an important reason why experts recommend replacing mascara three months after it’s opened.
Kelly Reynolds, Ph.D., assistant professor of public health at the University of Arizona, who was not associated with the study, explains that eyes are vulnerable to infection, with open pores where the eyelashes emerge, as well as glands and tear ducts.
Though mascara is the makeup item most commonly used beyond the recommended date, the women in the study also reported using eye pencils, lipsticks, lip glosses, eye shadows, face powders, foundations, and concealers past their expiration date. But, according to the study’s authors, expired mascara poses the greatest danger “because of the proximity and contact with [the eye] and thus, the higher probability of causing irritation or, if the product is contaminated, ophthalmic infections,” Women’s Health reports.
Women’s Health offers tips for protecting against makeup-related infections. The most important precaution is to replace mascara every three months, even if it isn’t used up. Never share makeup with anyone else; bacteria transferred from another person could make you sick. To slow bacteria growth, it’s best to store makeup away from the bathroom, usually warmer and more humid than other rooms, therefore more conducive to bacteria growth. Contact lens wearers should insert their lenses before applying makeup to avoid trapping bacteria from makeup behind the lens, where it can grow more rapidly.