Allergic contact dermatitis

Allergic contact dermatitis is a common skin condition caused by an allergic reaction to substances that come into contact with the skin. It primarily affects the skin, leading to symptoms such as redness, itching, and blistering. This reaction occurs when the immune system mistakenly identifies a harmless substance as harmful, triggering inflammation. The condition can develop after exposure to various allergens like metals, fragrances, or plants. It often appears on areas of the body that have direct contact with the allergen. The severity of symptoms can vary from mild irritation to severe discomfort. This condition impacts daily activities due to skin discomfort and visible rash.

Allergic contact dermatitis is a type IV hypersensitivity reaction characterized by a delayed immune response mediated by T lymphocytes against small reactive chemicals called haptens. These haptens penetrate the skin and bind to proteins, forming antigenic complexes that activate sensitized CD4+ and CD8+ T cells. The condition typically results from repeated exposure to allergens such as nickel, poison ivy (urushiol), or fragrances. Clinically, it presents as an erythematous, pruritic, vesicular rash localized to the site of contact. The pathophysiology involves a sensitization phase followed by an elicitation phase upon re-exposure. This immune-mediated inflammation leads to epidermal damage and characteristic skin lesions. It is a significant cause of occupational and environmental dermatitis.