Allergic contact dermatitis phases

SENSITIZATION PHASE.

Antigen is applied to the skin surface, penetrates the epidermal barrier (stratum corneum) and is taken up by Langerhans' cells in the epidermal basal layer. The antigen is “processed” and displayed on the surface of the Langerhans' cell. This cell migrates to the regional lymph nodes and presents the antigen to T lymphocytes. Cytokine-induced proliferation and clonal expansion within the lymph nodes results in T lymphocytes bearing receptors that recognize the specific antigen. These antigen-specific T lymphocytes enter the bloodstream and circulate back to the epidermis.

ELICITATION PHASE.

The elicitation phase occurs in sensitized patients with reexposure to the antigen. Langerhans' cells bearing the antigen interact with antigen-specific T lymphocytes that are circulating in the skin. This interaction results in cytokine-induced activation and proliferation of the antigen-specific T lymphocytes and the release of inflammatory mediators. Allergic contact dermatitis develops within 12 to 48 hours of antigen exposure and persists for 3 or 4 weeks.

Cross-sensitization

An allergen, the chemical structure of which is similar to the original sensitizing antigen, may cause inflammation because the immune system is unable to differentiate between the original and the chemically related antigen. For example, the skin of patients who are allergic to balsam of Peru, which is present in numerous topical preparations, may become inflamed when exposed to the chemically related benzoin in tincture of benzoin.

Systemically induced allergic contact dermatitis

Systemic contact dermatitis results from the exposure to an allergen by ingestion, inhalation, injection, or percutaneous penetration in a person previously sensitized to the allergen by cutaneous contact. Patients allergic to poison ivy develop diffuse inflammation following the ingestion of raw cashew nuts . Cashew nut oil is chemically related to the oleoresin of the poison ivy plant. Persons allergic to balsam of Peru and/or fragrance mix benefit from dietary avoidance of balsams