Scottsdale, Arizona - There’s something lurking at the bottom of your makeup bag, and it’s not pretty. According to Mary Duh, physician assistant, Dermatology, Mayo Clinic Health System, old and expired cosmetics harbor dangerous amounts of bacteria. This not only directly affects the individual wearing the makeup, but it also can affect anyone they come in contact with.

“Makeup can be infected with bacteria after only one use. The bacterium builds up over time and can cause harm to a person’s skin, eyes, lips and overall health,” says Duh. “When makeup gets old, it starts to break down, and this can cause issues from irritation and inflammation to rashes, blisters, eye infections and pink eye.”

In rare cases, women have been temporarily or permanently blinded by an eye cosmetic, according to the U.S. Food and Drug Administration.

Duh offers these rules for healthy cosmetic use:

• Look through your old makeup for chemical changes, including: a rancid odor, color change, changes in texture or consistency, and makeup becoming crusty or clumpy.
• Protect your skin from the sun. Most foundations have some level of sun protection factor. Expired makeup is less effective when protecting against the sun, which can cause painful and dangerous skin burns.
• Never share cosmetics. Cross-contamination occurs when two or more people use the same application tools and makeup. The main danger with sharing makeup is passing an infection or virus.
• Wash your hands and cosmetic tools before applying eye cosmetics. The bacteria on your hands and brushes increase the chance for an eye infection or allergic reaction.
• Don't store cosmetics at temperatures above 85 degrees Farenheit. For example, cosmetics held in hot cars for long periods of time, are more at risk of preservatives in the makeup weakening.
• When applying or removing eye cosmetics, be careful not to scratch the eyeball or some other sensitive area of the eye. Scratches can cause infections and sight complications.
• Date makeup when you buy it. Write the month and year on the package with a permanent marker. If you're not sure when to toss old makeup, six months is a good rule of thumb.