Table of Contents
Allergic Dermatitis Definition
Allergic dermatitis is a HYPERSENSITIVITY REACTION (allergic reaction) that affects the SKIN, usually in response to contact with an ALLERGEN. As with all hypersensitivity reactions, the first exposure to the allergen produces no symptoms. In reaction to the exposure, however, the IMMUNE SYSTEM produces antibodies for the allergen. Subsequent exposures to the allergen then do produce symptoms. Abundant immune cells reside in the epidermis, the inner layer of skin that contains living cells, to react to the allergen.
Most allergic dermatitis is a type IV, or delayed, hypersensitivity reaction. Symptoms generally affect only the area of contact and begin to emerge 24 to 36 hours after the contact, though may start within hours to a week later. Sometimes there can be repeated exposure before the hypersensitivity reaction occurs, though most commonly the second exposure triggers the ALLERGY.
A less common but more severe form of reaction is atopic dermatitis, a chronic type I (IMMUNOGLOBULIN E [IgE]) hypersensitivity reaction. Atopic DERMATITIS, commonly called eczema, tends to occur in people who have other chronic hypersensitivity conditions such as ALLERGIC ASTHMAand ALLERGIC RHINITIS. GENETIC PREDISPOSITION is the most significant risk factor for atopic dermatitis. Often there is no apparent contact allergen that sets off an atopic dermatitis attack, and symptoms may continue for several weeks to months or appear to never quite go away.
Poison IVY, Poison OAK, and Poison SUMAC
The blistering, itchy RASH that some people develop with exposure to poison ivy, poison oak, and poison sumac is an allergic reaction to the resins on the surface of these plants. Repeated contact creates as well as intensifies sensitivity. In a highly allergic person, a reaction may occur through contact with clothing that came into contact with the resins. Contrary to popular belief, the fluid in the rash’s blisters does not spread the irritation. The rash appears to spread because the person’s sensitivity to the resin increases even as the allergic reaction unfolds.
Symptoms of Allergic Dermatitis and Diagnostic Path
Allergic dermatitis, sometimes called allergic contact dermatitis, results in URTICARIA (hives) or RASH, often along with itching. BLISTER formation is common. The diagnosis is fairly straightforward when the person knows he or she has had contact with a known allergen. It is sometimes difficult to distinguish allergic dermatitis from other forms of dermatitis. In such situations ALLERGY TESTING, in which the allergist places small amounts of suspect substances in patches on the skin, can often determine the responsible allergen. Many substances, such as detergents and cleaning chemicals, can cause contact dermatitis through direct damage to the cells of the skin. Though symptoms are similar to those of allergic dermatitis, the irritation occurs as a direct action of the substance rather than as a hypersensitivity reaction.
Treatment Options and Outlook
Treatment may include calamine lotion and cool baths or compresses to relieve itching in combination with oral ANTIHISTAMINE MEDICATIONS or CORTICOSTEROID MEDICATIONS to interrupt the immune response. Cool baths or compresses with colloidal oatmeal can soothe irritated skin. Avoiding further exposure to the allergen prevents subsequent reactions and may, over time, allow the immune response to lessen in severity.
Risk Factors and Preventive Measures
Latex, nickel, chromates, and the dyes in permanent hair coloring solutions are the most common causes of allergic dermatitis. Numerous metal objects, including stainless steel and chrome plating, contain nickel. Spandex contains latex; spandex clothing such as undergarments and athletic wear may cause hypersensitivity reaction in people who are allergic to latex.
Chromates, chemicals used in tanning leather, are common in leather shoes, belts, and clothing. The allergen in permanent hair dyes is a chemical called paraphenylenediamine (PPDA), which sometimes is also present in some dyed clothing though is not commonly used in fabric dyes in the United States. The risk for allergic dermatitis is particularly high among people who work in jobs with constant exposure to these common allergens.