Oh yes they can. You “might” have figured out that I am a bit of a bacteria-phobe (see my web site at MRSAResources.com), and I cannot believe I haven’t addressed this issue yet, but I have been inspired, so here goes!

Cosmetics can be a breeding ground for bacterial growth, which can cause you problems ranging from nuisance blemishes to some downright ugly things that can leave you scarred for life (if you are lucky!). There is a fantastic article from INQ7.net titled To ditch or store – that is the question, and it is a very thorough article on what to do with your aging, and flat-out old cosmetics (hint–if they are in question, throw them away!). I could easily print the whole article for you here, as it is chock full of important information, but as I don’t have permission to do so, I will give you a snippet, and hope that you will read the rest at the link above.

*Foundation. Liquid formulations typically last three to six months. An oil-based foundation can last longer than water-based ones. Powders should last a year. If you can’t remember when you bought your foundation, one indicator that it’s gone bad is an offensive smell. You’ll also see an uneven or chunky consistency.
*Concealer. Because it’s exposed to the air and bacteria, replace concealer every three to six months.
*Blush. Powders usually last up to 12 months, and they can be kept longer than creams. Washing your blush brush often will keep the powder fresh longer. But always check for unpleasant smells or unusual consistency.
*Lipstick typically lasts up to two years, but throw it out when your favorite tube begins to smell. Extra tip: If you store lipstick in the refrigerator, it can last longer.
*Lip gloss. If you use your fingertips to apply it, toss it out after six months. A lip gloss that’s applied with a wand, however, can last up to a year.
*Lip liner. Every time you sharpen a lip liner pencil, you’re cleaning it. So if you’re sharpening it often, a lip liner can last indefinitely.
*Mascara. This is the one product that expires the quickest. Why? Of all makeup products, mascara is the most prone to microbial growth. Not only can expired mascara lead to eye infections, it also can dry out your lashes. Be sure to replace your mascara every three months. Extra tip: Don’t pump the wand in and out too much because it exposes the product to the air and potential irritants.