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Allergic Contact Dermatitis at a Glance
  • Allergic contact dermatitis (ACD) is a cell-mediated (type IV), delayed type, hypersensitivity reaction caused by skin contact with an environmental allergen.
  • Prior sensitization to a chemical 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 allergen in a sensitized individual will result in chronic disease, characterized by lichenified erythematous plaques with variable hyperkeratosis and fissuring that may spread beyond the areas of direct exposure.
  • Itch and swelling are key components of the history and can be a clue to allergy.
  • The hands, feet, and face (including the eyelids) are some of the common sites for ACD.
  • Patch testing is fundamental for the identification of causal allergens and is indicated for patients with persistent or recurrent dermatitis in whom ACD is suspected.
  • Avoidance is the mainstay of treatment for ACD. Educating patients about avoidance of the allergen and its potentially related substances, and providing suitable alternatives are crucial to a good outcome.

As the largest organ in the human body, the skin is a complex and dynamic organ that serves among many other purposes, the function of maintaining 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 at least 20% or more of the new incident cases in the subgroup of contact dermatitides (irritant contact dermatitis accounts for the remaining 80%).1 ACD, as the name implies, is an adverse cutaneous inflammatory reaction caused by contact with a specific exogenous allergen to which a person has developed allergic sensitization. More than 3,700 chemicals have been implicated as causal agents of ACD in humans.2 Following contact with an allergen, the skin reacts immunologically, giving the clinical expression of eczematous inflammation. In ACD the severity of the eczematous dermatitis can range from a mild, short-lived condition to a severe, persistent, chronic disease. Appropriate allergen identification through proper epicutaneous patch testing has been demonstrated to improve quality of life as measured by standard tools,3 as it allows for appropriate avoidance of the inciting allergen and possibly sustained remission of this 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.

A small but substantial number of 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 epidemiological studies on contact allergy in unselected populations including all age groups and most publishing countries (mainly North America and Western Europe). Based on these heterogeneous published data collected between 1966 and 2007, the median ...

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