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  • Allergic contact dermatitis (ACD) is a cell-mediated (type IV), delayed type, hypersensitivity reaction caused by skin contact with an environmental allergen.

  • Prior sensitization is required for allergy to develop.

  • The clinical manifestation of ACD is an eczematous dermatitis. The acute phase is characterized by pruritus, erythema, edema, and vesicles, usually confined to the area of direct exposure. Recurrent contact to the causative allergen may lead to chronic disease, characterized by lichenified erythematous plaques with variable hyperkeratosis, fissuring, and pigmentary changes that may spread beyond the areas of direct exposure.

  • Itch and swelling are key components of the history and may be clues to allergy.

  • Patch testing is the diagnostic test of choice to identify causal allergens and is indicated for patients with persistent or recurrent dermatitis in whom ACD is suspected.

  • Allergen avoidance is the mainstay of ACD treatment. Educating patients about avoiding the allergen and related substances, and providing suitable alternatives, are crucial to a good outcome.

The skin is a complex and dynamic organ that serves many purposes, among which is maintenance of a physical and immunologic barrier to the environment. Therefore, the skin is the first line of defense after exposure to a variety of chemicals. Allergic contact dermatitis (ACD) accounts for approximately 20% of new incident cases of contact dermatitis (irritant contact dermatitis accounts for the remainder).1 ACD, as the name implies, is an adverse cutaneous inflammatory reaction caused by contact with a specific exogenous allergen to which a person was previously sensitized. More than 3700 chemicals are implicated as causal agents of ACD in humans.2 Following contact with an allergen, the skin reacts immunologically so that in allergic individuals, such contact produces eczematous inflammation, which can range from a mild, short-lived condition to a severe, persistent, chronic disease, depending on the specific allergen and the amount, extent, and frequency of exposure. Appropriate allergen identification through proper epicutaneous patch testing improves quality of life as measured by standard tools,3 as it allows for avoidance of the inciting allergen and possibly sustained remission from the potentially debilitating condition. Recognition of the presenting signs and symptoms, and appropriate patch testing, are crucial in the evaluation of a patient with suspected ACD.


Several studies have investigated the prevalence of contact allergy in the general population and in unselected subgroups of the general population. In 2007, Thyssen and colleagues4 performed a retrospective study that reviewed the main findings from previously published epidemiologic studies on contact allergy in unselected populations of all age groups and from publishing countries (mainly North America and Western Europe). Based on these heterogeneous published data collected between 1966 and 2007, the median prevalence of contact allergy to at least 1 allergen in the general population was 21.2%. Additionally, the study found that the most prevalent contact allergens in the general population were nickel, thimerosal, and fragrance mix. The prevalence of ...

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