Contact dermatitis is a skin rash that results from contact with a substance that causes an allergic reaction. The rash usually starts within 48 hours of contact with the irritating substance. A minor reaction may cause mild redness of the skin or a rash of small red bumps. A more severe reaction may cause swelling, redness, and larger blisters.

Many things can cause contact dermatitis, including soaps, lotions, latex gloves, and plants such as poison ivy. The location of the rash may provide a clue about the cause.