Trash after two years:

Hairstyling products: If your products are packaged in a tube, spray, or bottle, they should last awhile. But if you're using products from a jar or tub, watch out. According to Min Kim, L'Oreal Portfolio Artist and hairstylist at Butterfly Studio Salon, these products don't last as long because they get exposed to the air and your germy fingers, which means they can dry out and get contaminated.

Shampoo and conditioner: Since water and air can break down the active ingredients in shampoo and conditioner, you'll want to keep lids tightly closed, says Kim. However, unused products will last a couple of years if they haven't been exposed to extreme heat (read: steamy showers) or sunlight.