Contact dermatitis is an example of which type of hypersensitivity?

Contact dermatitis is classified as a Type IV hypersensitivity reaction, also known as delayed-type hypersensitivity. This type of hypersensitivity does not involve antibodies but rather is mediated by T lymphocytes (T cells). In contact dermatitis, the body reacts to a specific allergen, such as poison ivy or certain metals, after a sensitization phase. During this phase, T cells are activated upon first exposure to the allergen, leading to the development of immunological memory.

Upon re-exposure to the same allergen, these memory T cells mount an immune response, resulting in inflammation and tissue damage at the site of contact. The delayed nature of this reaction typically manifests 24 to 48 hours after exposure, distinguishing it from other types of hypersensitivity, which may involve immediate reactions or mechanisms like antibody formation. This explanation highlights the specific immunological processes involved in contact dermatitis, clarifying why it is categorized as a Type IV hypersensitivity reaction.