Ancient Egyptians — both men and women -- smudged a dark substance called kohl around their eyes and applied henna to their skin as cosmetics.

Ironically, while a lot of this makeup contained toxic levels of lead, the heavy metal also helped ward off bacterial infections and may have kept King Tut from getting sick.

Today, things are reversed. While cosmetics are lead-free, many can act as vectors for potentially serious infections.

A study published in the Journal of Applied Microbiology found that 79% to 90% of in-use makeup has become contaminated with infectious microbes, including E.coli, staphylococci, and fungi, which can trigger rashes, skin and respiratory infections, and gastrointestinal issues.

How does this happen? Many users don't make sure their hands are clean before applying makeup, and they never clean the sponges and brushes used to for application.

In fact, 64% said they drop them on the floor and reuse them without a thought.

Foam sponges are especially vulnerable because they absorb moisture that can be a breeding ground for bacteria. 

To avoid infections, frequently clean cosmetic brushes and sponges with soap and warm water. Avoid dipping fingers directly into bottles or onto powders/blushes, as that can introduce bacteria into the product.

In addition, be mindful of a cosmetic's expiration date. Foundations are generally good for less than a year.

Eye makeup like mascara and eyeliner should be replaced every four months to avoid eye infections.

Lipstick and lip gloss should be replaced every six months, or more often.

And trust your senses. If something seems wrong, toss it out.