Here’s a HEALTH magazine article that, even though it dates back to 2000, is still relevant today.
I found these guidelines very helpful, and have always wondered when it was time to make the ultimate decision
of having to toss out that old makeup.
When it comes to your makeup bag, remember this rule: Use it or Loose it. Cosmetics aren’t required to carry
an expiration date, but they can still go bad. At best they won’t work as well; at worst they may irritate skin or
cause an eye infection. Lotions, creams, gels, and other water-based cosmetics are more likely than powders
to attract moisture-loving bacteria. But the clock starts ticking the moment any makeup product is opened and
exposed to air and light. To make yours last longer, keep caps tightly sealed, and store containers away from
heat and sunlight. To be safe, follow the “toss by” tips below.