Next to fragrances, preservatives found in cosmetic and skin care products are the most common allergens and irritants for people with sensitive skin [source: Mayo Clinic].
Any product that contains oil and water must also contain some kind of preservative to keep bacteria and fungi from forming. Since most skin care products contain either oil or water, it's hard to find one that doesn't contain preservatives.
Some of the most common preservatives found in cosmetic and skin care products are paraben, imidazolidinyl urea, Quaternium-15, DMDM hydantoin, phenoxyethanol, methylchloroisothiazolinone, and formaldehyde. All have been associated with skin allergies [source: WebMD].
If you discover that you're allergic to a preservative, there are preservative-free products available on the market, but they're a little harder to find. Some preservative-free products include an expiration date or must be stored in the refrigerator.