Which type of dermatitis is a delayed hypersensitivity reaction?

The type of dermatitis that is classified as a delayed hypersensitivity reaction is allergic contact dermatitis. This condition arises when the skin comes into contact with a substance that the immune system recognizes as foreign, leading to an immune response that involves T cells. Unlike immediate hypersensitivity reactions (such as those seen in atopic dermatitis), which occur swiftly, delayed hypersensitivity reactions typically take 24 to 48 hours to develop after exposure to the allergen.

Allergic contact dermatitis often presents with symptoms such as redness, swelling, and itching at the site of contact. The delayed nature of the immune response is a hallmark of this condition, which allows for the identification of specific allergens through patch testing.

In contrast, atopic dermatitis is more associated with immediate hypersensitivity mechanisms and is often linked to genetic factors and environmental triggers rather than direct allergens. Seborrheic dermatitis is primarily a chronic inflammatory condition associated with an overgrowth of Malassezia yeast and does not involve an immune-mediated hypersensitivity reaction.