Definition and epidemiology:

Allergic contact dermatitis (ACD) is a delayed type hypersensitivity reaction that is elicited when the skin is exposed with a substance to which an individual has been previously sensitized. Allergic contact dermatitis accounts for 20% of the contact dermatitis, and it can affect individuals in all walks of life.

Pathogenesis:

Allergic contact dermatitis is a T-cell mediated, delayed type hypersensitivity reaction. It’s an allergen-specific reaction that requires prior sensitization of the individuals to the chemicals. The pathogenesis involves 2 phases in which the initial sensitization phase when the individual comes in contact with the chemical, which penetrates the skin and triggers a cascade of events that leads to sensitization. The subsequent re-exposure of the skin leads to the presentation of the responsible allergen to the primed T-cell, causing release of multiple cytokines resulting in the clinical picture of eczema.

Clinical features:

Acute allergic contact dermatitis presents with erythematous, indurated, scaly plaques. Vesicle and bullae formation may occur in severe cases.

Repeated or continuous exposure to the allergen results in chronic disease. The skin becomes dry, scaly and thickened as a results of acanthosis and edema.

Allergic contact dermatitis is typically localized to the area in which the skin is exposed to the chemical. For example:

Allergens applied to the scalp including hair dies and shampoos may elicit dermatitis in that area
Facial lesions may results from contact with cosmetic products
Dermatitis involving the dorsal aspect of the foot suggests allergic contact dermatitis related to the shoe chemicals (rubber accelerators or potassium dichromate)
Periorificial allergic contact dermatitis involving the perioral, periocular and genital areas may be induced by fragrances, detergents or preservatives in hygiene products (moist wipes).

Diagnosis:

Clues from the clinical examination: The morphology, location and the course of dermatitis supports the diagnosis of allergic contact dermatitis. The typical appearance is well demarcated, pruritic, eczematous eruption localized to the area of skin that comes in contact with allergen.

History: A comprehensive history is helpful in aiding the diagnosis of allergic contact dermatitis. This includes reviewing the patient’s activities, hobbies, occupation and products used by the patient.

Health professionals, chemical industry workers, beauticians and hairdresser have an increased risk of developing occupational allergic contact dermatitis. A history of improvement during the weekends and holidays suggests an occupational origin.

Patch test: patch test is essential investigation in patients with persistent eczematous eruptions when contact allergy is suspected or cannot be ruled out. Patch test is based upon the principle that in sensitized individuals, primed antigen specific T lymphocytes circulating throughout the body and are able to recreate a delayed type hypersensitivity reaction when non irritating concentrations of the antigen are applied to normal skin.

Treatment:

Once the antigen has been identified, the patient should be given written information about the chemicals. The information sheet should include the name of the chemical, synonyms, typical uses, how to avoid exposure and alternatives.

Although avoidance of the allergens is the mainstay of treatment, pharmacological treatment is required to achieve rapid control of symptoms in most cases. The treatment of allergic contact dermatitis follows the general principles of treating eczema including:

Emollients
Topical corticosteroids
Topical calcineurin inhibitors such as tacrolimus
Phototherapy (PUVA, narrow band UVB)
Systemic immunosuppressants such as azathioprine and methotrexate

Written by:

Bandar Alharbi, Medical Intern

Revised by:

Naif Alshehri, Medical Intern

Resources:

Dermnet

Uptodate

Bolognia