Allergic Contact Dermatitis

Abstract

Allergic contact dermatitis develops owing to a delayed type cell-mediated sensitization to contact with exogenous factors. It is essentially localized at the site of exposure to the noxa and is accompanied by variable pruritus. It seems that some subjects are more prone to sensitization to environmental allergens than others, even if the total number of sensitized individuals in a population depends on the degree of skin exposure. The morphological picture features a remarkable polymorphism as regards the clinical signs, type of eruption and evolution. The objective manifestations of the classic picture differ according to the clinical phase of the disease: the acute form manifests with erythemato-edemato-vesicular patches with blurred margins. In the subacute phase, puntiform scubs appear while the erythema and exudation decline. Infiltrative plaques will appear in the chronic form. Other clinical-morphologic varieties are frequently observed: lichenified eczema, hyperkeratotic eczema, nummular contact dermatitis, and dry eczema of the hands. It is not usually easy to trace the culprit substance based on the clinical picture, although some clinical patterns can indicate a particular group of substances, or even a specific allergen. A particular characteristic of allergic contact dermatitis is the presence of lesions at a distance from the primitive focus where the original contact with the hapten occurred (“idic” eruptions). The spread of contact dermatitis, that can even progress as far as a picture of erythroderma, can be caused by multiple factors (chronic contact with the allergenes responsible, inappropriate topical or systemic treatments, poly- and cross-sensitization). Regarding the aetiopathogenic assessment, it is important to take into account factors such as polysensitization, co-sensitization, and cross-sensitization. As regards the evolution of the dermatitis over time, there are various possibilities. The diagnosis is based on clinical and allergological (patch tests) criteria. Excluding the rare and serious erythrodermic condition, the prognosis is favorable, also in terms of the patient’s quality of life.