Clinical features and diagnosis of allergic contact dermatitis

Allergic contact dermatitis - Subumbilical allergic contact dermatitis from metal fasteners in pants (nickel allergy).


● Allergic contact dermatitis (ACD) is a T-cell-mediated, delayed-type hypersensitivity response to exogenous agents. Contact allergens may be found at home or in the workplace and may include metals, glues, plastics, rubber, fragrances, topical antibiotics, preservatives, and chemicals used in hair care and cosmetic products.

● Acute ACD lesions consist of pruritic, erythematous, indurated, scaly plaques, typically localized to the skin areas that come in contact with the allergen (picture 1A-C). Vesiculation and bullae may be seen in severe cases (picture 2). Edema of the eyelids, lips, and genitalia may be prominent (picture 3). In chronic ACD, the skin is dry, scaly, and thicker. Lesions are typically localized in the skin areas that come in contact with the allergen (picture 6A-B).

● The source of contact allergens can be identified through a detailed review of the patient’s exposures at home and in the workplace (table 1).

● The clinical diagnosis of ACD is based upon the lesion morphology and distribution. The involvement of hands, feet, eyelids, and lips, which most commonly come in contact with the environment, suggest the diagnosis of ACD. However, patch testing may be required to confirm the diagnosis and differentiate ACD from other types of eczematous dermatitis (table 2).

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