NEW YORK (CBSNewYork) — Makeup can be costly. And if you’re the type who likes to make it last as long as possible, you may be taking chances with your health.

If you dig through your cosmetics, you’ll probably find things that need to go. But how can you tell when your makeup bag needs a makeover?

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“I’ve seen it on the packaging,” Mia Gradney, a former makeup salesperson, told CBS2’s Emily Smith. “Have I ever really paid it any attention? No.”

The expiration date is on a picture of a jar located on the packaging, marked with a number next to the letter M – for months.

Dermatologist Dr. Lisa Hitchins explains:

“What that means is it’s the period after opening, or PAO,” Hitchins said. “Once this is opened you have 24 months to be able to use it safely.”

If you don’t toss the old stuff, you could end up with some problems you don’t want.

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“You could get E. coli, you could get staph, you could get Pseudomonas,” Hitchens said. “Pseudomonas is an infection very common in eyes and ears — when people get swimmer’s ear, that’s usually Pseudomonas.”

Dr. Hitchins also shares another little secret: On the packaging of many products, you’ll find a batch number — plug that into the website checkfresh.com.

“It will come up…and it will tell you when it was made,” Hitchins said.

Cosmetic companies aren’t required to use expiration dates, so here’s a quick shelf life list:

Lotion, powder, blush, lipstick typically expires after two years. Foundation, lip gloss, and nail polish will be done in just one year.

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Then there’s mascara. It lasts 4 months, tops — even less if you pump the wand. Experts say swirling will keep the air out and the contamination from getting in.