Kontaktiallergia

Kontaktiallergia, or contact allergy, is a type IV hypersensitivity reaction of the skin triggered by exposure to specific allergens. Sensitization occurs after the first contact, and on subsequent exposure the immune system mounts a T-cell–mediated inflammatory response at the site of contact. The reaction typically develops 24 to 72 hours after exposure and may last for days. It is distinct from irritant contact dermatitis, which does not involve an adaptive immune response.

Pathophysiology involves antigen-presenting cells processing small molecules (haptens) that bind skin proteins. These complexes are presented to T cells in regional lymph nodes, leading to memory T cells that mediate inflammation upon re-exposure. Cytokines recruit inflammatory cells, resulting in an eczematous eruption that may be pruritic and vesicular.

Common allergens include nickel (often in jewelry and belt buckles), fragrances, fragrances in cosmetics, latex, rubber accelerators, preservatives, cobalt, chromium, p-phenylenediamine (hair dyes), and epoxy resins. Sources are widespread in jewelry, clothing, cosmetics, household products, and occupational materials.

Clinical presentation is typically localized to the contact area and includes redness, itching, swelling, vesicles, and sometimes weeping or crusting. Chronic exposure can lead to thickened or lichenified skin.

Diagnosis relies on patch testing to identify relevant allergens. The test is read at multiple time points, commonly at 48, 72, and sometimes 96 hours, with results interpreted in the context of exposure history.

Management centers on avoidance of identified allergens, use of barrier protections (such as non-nickel and fragrance-free products), and treating inflammation with topical corticosteroids and emollients. Severe cases may require systemic therapy or occupational adjustments. Prognosis improves with effective allergen avoidance; relapses occur if exposure resumes.