It has now been found that N-L-alpha-aspartyl-L-phenylalanine 1-methyl ester (APM) and/or one of its lower alkyl derivatives can be used to treat allergic contact dermatitis associated with irritating oils such as catechol-containing plant-derived antigens such as poison ivy, poison oak, poison sumac and Asian lacquer tree and oils containing capsaicin. Topical application of APM and/or derivative can reduce or alleviate the symptoms associated with irritation of the skin and/or mucous membranes caused by contact or inhalation of these oils or fumes from burning vegetation containing these oils.