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Cosmetic preservatives are second only to fragrances as the most common cause of skin reactions, according to the American Academy of Dermatology. But preservatives are necessary components of most personal-care products, says Zoe Diana Draelos, M.D., clinical associate professor of dermatology at Wake Forest University School of Medicine. 'Preservatives are there not only to keep the makeup fresh on the shelf, but also to prevent you from contaminating the product," Draelos says.

Some preservatives, however, present unnecessary health risks. When shopping, look on labels for the following:

Common Preservatives to Avoid

The Food and Drug Administration (FDA) requires listing most ingredients on labels but does not conduct safety tests. While some of the chemicals below have been tested and deemed "generally recognized as safe" by the Cosmetic Ingredient Review (CIR), an industry-funded organization, other, independent studies have raised cause for concern.

• Butylated hydroxyanisole (BHA): Used mainly in lipsticks and eye makeup, BHA is "reasonably anticipated to be a human carcinogen," according to the U.S. Department of Health and Human Services 2005 11th Report on Carcinogens. It's also been found to trigger contact dermatitis.
• "Formaldehyde" Preservatives (diazolidinyl urea, DMDM hydantoin, imidazolidinyl urea, quaternium-15 and bronopol) (sometimes listed as 2-bromo-2-nitropropane-1,3-diol): These preservatives either contain, release or break down into formaldehyde, a known human carcinogen and neurotoxin as well as skin irritant. Bronopol, when combined with other ingredients such as triethanolamine (TEA), diethanolamine (DEA) or the sunscreen chemical PABA, can contribute to the formation of cancer-causing nitrosamines, according to the FDA.
• Grapefruit seed extract (GSE): While consumers may think they're purchasing a "natural" product, seven out of nine samples of GSE preservatives contained either benzethonium chloride, a suspected hormone disruptor, or benzalkonium chloride, a skin and eye irritant, a May 2006 study in the Journal of Agricultural and Food Chemistry found.
• Kathon CG (sometimes listed as methylchloroisothiazolinone): Highly irritating to skin.
• Mercury (thimerosal): The FDA has allowed neurotoxic mercury to be used as a preservative only in eye makeup at concentrations no higher than 65 parts per million (ppm), "provided no other effective and safe preservative is available for use." Yet the federal government has established a maximum consumption level for mercury of one ppm. Mercury is readily absorbed through the skin.
• Parabens (methyl-, propyl-, butyl- and isobutyl): In addition to being suspected hormone disruptors, these chemicals have been shown to cause chronic dermatitis and are irritating to the eyes.

Safer Alternatives

The chemicals below have shown no deleterious health effects in non-CIR studies thus far, and the CIR has published its safety data on these ingredients in peer-reviewed journals.

• Sorbic acid/Potassium Sorbate: While potentially irritating, especially in eye makeup, these preservatives have demonstrated no other detrimental human health effects.
• Tocopherols (vitamin E): CIR found that these preservatives have very little potential to irritate skin and pose no additional health threats.
• Ascorbic acid (vitamin C) compounds (L-Ascorbic Acid, Magnesium Ascorbyl Phosphate, Sodium Ascorbate and Sodium Ascorbyl Phosphate): These have shown little risk of skin sensitization and no toxic effects.
• Essential oils: Many companies are using essential oils with inherent antimicrobial and antibacterial properties, such as lavender, rosemary, rose, thyme and tea tree oils, to preserve cosmetics. Tea tree and lavender oils, which have estrogenic properties, have been linked to enlarged breasts in young boys. Parents should avoid these ingredients in children's personal care products. Other essential oils haven't been independently tested for safety or efficacy, therefore it's important to follow expiration dates or the time guidelines listed below.