Methylchloroisothiazolinone/methylisothiazolinone is a preservative found in cosmetic and industrial products, and is a common ingredient in moist toilet paper. It is a well-known allergen and is capable of causing allergic contact dermatitis.We present the case of a 58-year-old white woman with a cutaneous vulvar eruption with associated discomfort and pruritus of 6 months in duration. She had been treated with antibiotic and antifungal agents without improvement of symptoms. Careful history taking revealed that the patient was using moist toilet paper. Patch testing confirmed an allergy to methylchloroisothiazolinone, a preservative in the moist toilet paper. After discontinuation of the product and treatment with potent topical steroids, the eruption completely cleared.With the growing use of moist toilet paper among adults, the risk of exposure and potential sensitization is increasing. Health care providers should be aware of the risks of moist toilet paper containing potential allergens because perianal and perineal dermatitis caused by these products may be unrecognized or misdiagnosed. After proper treatment, patients must be educated about alternatives and the importance of label reading.