Should I be afraid of three-year-old shampoo?

Hello, Matt:

I was going through that scary area under my bathroom sink the other day and found a bottle of shampoo I had purchased two or three years ago. It got me to wondering, does stuff like that have a shelf life? How 'bout toothpaste, hairspray, deodorant, soap?

-- Marina, from net LA-La-Land

Shampoo might not have the shelf life of Twinkies or Lucky Charms, but it can hide out under your sink, unopened, for at least two years without big risks. It might be a little thick and goopy or smell funny, but it won't make your hair fall out. The FDA doesn't require expiration dates on cosmetic products with a shelf life of three years or more. And they define "cosmetics" as any product "applied to the human body for the purpose of cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body's structure or function." Soap, non-medicated shampoo, mouthwash, and bubble bath are cosmetics. Dandruff shampoo, deodorants, sun blocks, tanning aids, and fluoride toothpaste are not. It's not so much that three-year-old deodorant will fry your pits or anything. It's just that some of the ingredients may have lost their effectiveness by then.

As for oil-based facial cosmetics, the FDA warns that they can go rancid within six months. You transfer skin bacteria into the products too, so they can be festering pits of microbes. Even the manufacturers admit a mascara wand is a deadly weapon after just three months.