Newswise — Is your mascara clumpy? Your liquid foundation thickening? Can't remember what year you bought your half-used lipstick? Dermatologists say your old makeup may be causing you blemishes or even worse—it could lead to a dangerous infection.

"Most women do have a drawer full of cosmetics that have been partially used," says Angela Bowers, M.D., dermatologist on the medical staff at Baylor Regional Medical Center at Grapevine.

Those old makeup containers may be full of more than just powder, they could be harboring dangerous bacteria. So how do you know when to throw them out?

"It's difficult to know because cosmetics usually don't include expiration dates," adds Dr. Bowers.

Experts say you should go by when you first opened the makeup. Eye make-ups and liquid foundations last the least amount of time and should be tossed out after just three months.

"The bacteria can get in there and the preservatives might not be working quite as well as they were when you first opened it. If you get some of that in your eye you may develop conjuctivitus which we know as 'pink-eye,'" explains Dr. Bowers.

Powders and foundations opened more than a year ago can also cause problems.

"Some women may develop a peri-oral dermatitis from using some old, expired makeup that might irritate the skin and cause little red bumps that look like acne," adds Dr. Bowers.

In addition to makeup, makeup applicators should be replaced regularly as well.

"If you use sponges to apply makeup, you should replace those at least once a week," says Dr. Bowers.

It may be painful for most women to throw out expensive products, but not doing so could hurt worse.

"If you end up in the doctor's office with an infection, all those savings are negated. You always want to have a clean face with some good, fresh product on there," adds Dr. Bowers.

Also, sharing lipsticks is another way that makeup can cause health problems. Sharing lipsticks, lip glosses or lip balms with someone who may have a strain of the herpes virus could leave you with cold sores of your own. Remember, people can harbor this particular virus on their lips without having an active cold sore so it will not always be visible.

If makeup looks old or changes texture is it a good idea to throw it out?

Yes, experts even advise to smell your makeup. An unusual odor usually means that it contains bacteria.

For more information about Baylor Regional Medical Center at Grapevine, visit