Contact dermatitis is a condition that makes skin red or inflamed after contact with a particular substance. Contact dermatitis is either the result of an allergen or an irritant. Allergic dermatitis usually appears between 12 and 72 hours after exposure. Contact dermatitis usually takes additional time to develop, but strong irritants can cause immediate discomfort and possibly skin damage. Substances that commonly trigger contact dermatitis are perfumes, chemicals, and plants like poison ivy and poison oak.