When the skin changes are a direct result of exposure and allergic mechanisms are not involved, the rash is termed irritant contact dermatitis. Atopic individuals are particularly susceptible. Even when a period of avoidance produces healing, chronic irritant dermatitis rends to recur readily with re- exposure. Allergic contact dermatitis Allergic contact dermatitis is the response to a substance to which the individual has become sensitised. Contact allergic dermatitis usually begins at the site of contact.
Many factors determine the acquisition of contact allergy.
Once initiated, repeated exposure tends to produce increasingly severe and widespread dermatitis, and sites far removed, such as the eyelids, can be involved. The allergic state usually persists for life. A positive reaction does not prove the cause of a patient's rash, but does help confirm suspicions and suggest unsuspected materials.