Beauty bag rehab: When's the last time you cleaned out your makeup stash and started fresh?

Even if you can make your favorite eyeliner last a year or more, it doesn't mean you should. Makeup has a shelf life, and time and temperature cause the ingredients to break down and lose effectiveness. Makeup also can be a breeding ground for bacteria.

"The products can separate or get an odor to them," says Lindsey Kielas, a nail technician and makeup artist at The Hair Loft Salon & Spa in Cape Girardeau. "You don't want to chance it. If you notice a smell or if [the product] starts to separate or clump in any way, then it's probably time to throw it out."

Cynthia Williams, makeup consultant at Concepts Styling Salon in Cape Girardeau, says all makeup should be replaced after six months to a year of use. Eye makeup, especially mascara, should be replaced every three months, or sooner if you've had an eye infection. Never share your eye makeup, and when a tube of mascara starts to dry out, it's time to replace it.

Lip gloss and lipstick can be used for two or three years, but again, you should probably replace lip products after you've been sick.

If you wear products with an SPF, they need to be replaced within a year after opening, as SPF will not properly protect from the sun past its expiration date (the date should be printed somewhere on the container). Powder makeup formulas with SPF can be used longer than liquid forms, says Kielas.

Shampoo and conditioner usually have a shelf life of two years, she adds, though most people use up their hair products long before that. However, if you're a coupon queen with a giant stockpile of shampoo and conditioner, Kielas and Willams warn that any expired products may lose effectiveness if kept for too long.

It's also important to protect beauty products from the elements if you want to glean as much use from them as possible.

"With hair products and makeup, you should never, ever, ever let them get too warm or hot. The ingredients break down and you're not going to be able to use them as well," says Williams.

Makeup brushes also need care and replacement.

"You should wash your brushes about every three months to keep them fresh and then replace them within about a year -- that's about the life of a brush that you're using every day," says Williams.