When does ACD occur?

When contact w/ a particular substance elicits a delayed hypersensitivity reaction, sensitization requires 10-14 days, and when re-exposure occurs dermatitis appear w/in 12-48 hours. Most common cause is Rhus Dermatitis (poison Ivy/Oak/Sumac) Other causes topic Abx, benzocaine, Vitamin E, Rubber, Nickel, Formaline, Preservatives (some skin care products), Fragrances.