Allergic contact dermatitis is an itchy skin condition caused by an allergic reaction to material in contact with the skin. It arises some hours after contact with the responsible material, and settles down over some days providing the skin is no longer in contact with it.
Contact dermatitis should be distinguished from contact urticaria, in which a rash appears within minutes of exposure and fades away within minutes to hours. The allergic reaction to latex is the best known example of allergic contact urticaria.
Allergic contact dermatitis is also distinct from irritant contact dermatitis, in which a similar skin condition is caused by excessive contact with irritants. Irritants include water, soaps, detergents, solvents, acids, alkalis, and friction. Irritant contact dermatitis may affect anyone, providing they have had enough exposure to the irritant, but those with atopic dermatitis are particularly sensitive. Most cases of hand dermatitis are due to contact with irritants.
Allergy is the term given to a reaction by a small number of people to a substance (known as the allergen) which is harmless to those who are not allergic to it. Only small quantities of allergen are necessary to induce the reaction. Contact allergy occurs predominantly from the allergen on the skin rather than from internal sources or food. The first contact does not result in allergy; often the person has been able to touch the material for many years without adverse reaction.
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