Are you still hanging on to the lipstick you wore to your senior prom because it's the perfect shade of red? Or maybe you only wear mascara for special occasions so you've had the same bottle for years? And why buy a new blush brush when the one from the '90s still works fine? Think again! (But take comfort in knowing that you're not alone: One woman in the audience has had the same lipstick for 30 years!)

"Makeup doesn't get better with age," says beauty expert Sonia Kashuk. "We do, but makeup doesn't." Sonia explains that makeup has a "P.A.O." -- a period after opening, which is the amount of time your makeup will last after the first use. Since makeup doesn't come with an expiration date written on the product, Sonia suggests that once you open a new lipstick or bottle of mascara, label it with the date so you know when it's time to throw it out.

So how long is too long when it comes to makeup?

Eye Products

You shouldn't keep mascara longer than six months. The same goes for products such as eyeliners, eye pencils and concealer -- they're a breeding ground for infection, so six months is the maximum P.A.O.

Lipstick

The P.A.O. for lipstick is a little bit longer than that of mascara -- you can use it for up to two years.

Brushes and Sponges

"You really need to wash them regularly," Sonia says. "I go to my kitchen sink and use whatever soap is there. And the most important thing is to lay the brush flat to dry so that the shape doesn't change. You wake up in the morning and you're ready to go!"

Other Tips

• Store your makeup in a cool, dry place.

• Beware when you visit those makeup counters in department stores where they offer free testing -- you don't know where those products or brushes have been or who they've been used on!
• There's no difference in the P.A.O. between your average-priced makeup and top-of-the-line beauty products. All makeup has a shelf life no matter how much you pay for it.