Contact dermatitis is inflammation of the skin caused by contact with a substance that causes an allergic reaction. A minor case of contact dermatitis may cause mild redness of the skin or a rash of small red bumps, while a more severe reaction may cause swelling, redness, and larger blisters.
A rash usually starts about 48 hours after exposure to the irritating substance. Common causes of contact dermatitis include:
The location of the rash may provide a clue about the cause.
Contact dermatitis does not usually occur with the first exposure to the irritating substance (allergen). Once a reaction to the substance occurs, a rash can occur in response to even very small amounts of the substance.
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