The sap of the plant Agave americana, incorrectly named "cactus juice" and used as a "hair restorer," evoked contact urticaria followed by acute eczematous dermatitis of the skin of the scalp, forehead, and wrist. Open patch tests with fresh sap produced burning pain, follicular contact urticaria, and subsequent irritant dermatitis in the patient and in two control subjects.
Kerner J, Mitchell J, Maibach HI. Irritant Contact Dermatitis From Agave americana LIncorrect Use of Sap as "Hair Restorer". Arch Dermatol. 1973;108(1):102-103. doi:10.1001/archderm.1973.01620220064017