If you've been using the same eyeshadow palette or lipstick since high school, or your cosmetics aren't working as well as they used to chances are a lot of the products in your collection are expired. The shelf life of common beauty products might be shorter than you think, meaning that many of your products could be swimming in bacteria which could cause skin irritation or eye infections.

While most makeup products don't contain a specific expiration date, many people don't know that some products contain a PAO (Period After Opening) symbol which identifies the lifetime of your favorite products. The PAO symbol can be found on the label of products and looks like a small jar with the lid open containing a number, followed by the letter "M" for months. "6M" for example means that the product is best if used before the end of 6 months, whereas "24M" means the product should be used up before 2 years. Although these are only guidelines and the shelf life can be shortened depending on usage and storing conditions.

A general rule of thumb is that liquid products have a shorter shelf life than most powder products.

Foundation: 3-6 months
Mineral makeup: 6 months (these often don't contain the same preservatives)
Concealer: 6 months
Stick Concealer: 12 months
Powder/Blush: 12-24 months
Lipgloss/Lipstick: 12-18 months
Mascara: 3-6 months (be sure to toss if you develop an eye infection, and don't pump)
Eye Cream: 6 months
Eye pencils: 12-24 months (sharpen often)
Eye Shadow: 12-24 months

Note: If any of your products have spoiled, separated or smell rancid it's a good idea to toss.

When in doubt toss it out.