Allergic contact dermatitis from cosmetics is a common problem that is occasionally caused by new or rare allergens. When a patient has a positive patch test to a cosmetic product but to none of the common or commercially available allergens, it is important to further patch-test this patient to the ingredients of the product. Thorough testing with the breakdown of ingredients, usually obtained through cooperation with the manufacturer, often allows identification of the culprit allergen in the cosmetic product. In this article, we discuss emerging or rare allergens discovered by this method, including nail lacquer and lipstick allergens, copolymers, shellac, alkyl glucosides, glycols, protein derivatives, idebenone, and octocrylene.