Silva: The cosmetic companies they work for train them to say those things because these companies are liable for people that get sick or suffer from any damages; there are safety regulations put in place they must follow.

SM: What do we need to know about makeup brushes and keeping our products clean?

Silva: You should never let your makeup brush, finger or any other applicator go into the actual container. There’s bacteria that will grow and contaminate the makeup, which leads to breakdown. Makeup artists are taught to offload makeup onto a palette and then dip the applicator into it so that you’re not cross-contaminating the makeup. Secondly, you should absolutely clean your brushes as often as possible—every time you use them. If not, set a time once every couple of days or once a week to do so. 

Author’s Note: To properly clean brushes, hold head down at an angle under warm running water. Lightly massage a gentle cleanser such as baby shampoo in the direction of the bristles (many beauty stores also sell special cleaning sprays). Rinse until no more color runs out and gently squeeze out excess water using a clean, dry towel. When finished, reshape brush with fingers into the original shape. Let air dry overnight, either lying flat or upside down.
 
SM: How can we tell when it’s time to toss our foundation?