Delayed-type hypersensitivity

Delayed-type hypersensitivity (DTH) is an immune response that occurs hours to days after exposure to an allergen or foreign substance. It involves immune cells called T cells, which recognize the substance and release chemicals that cause inflammation and tissue damage. This reaction is responsible for conditions like contact dermatitis and positive skin allergy tests. Unlike immediate allergic reactions, DTH takes time to develop, as it requires T cell activation and recruitment to the site of exposure, leading to localized swelling, redness, and sometimes blistering or skin irritation.