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.

Women throughout history have used makeup to enhance their beauty. The first recorded evidence of makeup being used was from the ancient Egyptians who wore foundation to lighten their skin, and kohl eyeliner.

• The eye kohl, made of lead and burnt almonds, was used to outline the eyes and was thought to ward off evil spirits and improve eye sight.

• During the Italian Renaissance Aqua Toffana, a popular face powder, was instructed to be used by the rich when their husbands were around. Made from arsenic, the powder was highly poisonous, which is where the phrase “kiss of death” comes from. The creator, Toffana,  was later executed after it resulted in the death of over six hundred dead husbands.

• During Elizabethan England women wore egg whites over their faces to achieve a glazed look.

• During the Regency era, white skin was ideal showing a life of leisure and tanned skin was frowned upon indicating a life of hard outdoor labor. Women went through great lengths to cover their bodies and faces with whiteners (often containing lethal ingredients) to achieve this look.

• During the victorian era, makeup was used primarily by prostitutes and actors (who were thought to be the same thing.) Queen Victoria publicly declared makeup improper, vulgar, and unacceptable.

• During the 1920's. Newly emancipated women in America showed their independence and freedom by using bright red lipstick, which was often scented with cherry.

• The suntan look was initiated by Coco Chanel who made it fashionable, this caused dozens of new fake tanning products to be produced to help achieve the sun-kissed look.

In recent years makeup usage and sales have increased rapidly with more makeup products in the world today then any of us could probably use in a lifetime. Thankfully for us, though, the FDA regulates what goes in our products.