The etiology of cheilitis is often not readily apparent. We present a case series of four patients with allergic contact cheilitis (ACC) secondary to exposure to peppermint oil contained in a lip balm product. These patients developed eczematous dermatitis involving their lips and perioral skin. They were tested with the North American Contact Dermatitis Group standard series as well as with an expanded series of flavoring agents, sunscreens, plant and fragrance components, and their own products. The lip balm contained potential sensitizers such as propolis, lanolin, coconut oil, almond oil, peppermint oil, and vitamin E. Our patch-test results showed that peppermint oil was the most likely culprit in these patients' ACC. Peppermint oil is less commonly reported as causing ACC than are more common contactants such as balsam of Peru or nickel sulfate. However, with the widespread use of lip balms containing peppermint oil, more cases of peppermint oil-induced ACC may be expected.