Contact dermatitis is an example of which type of hypersensitivity reaction?

Contact dermatitis is classified as a Type IV hypersensitivity reaction, which is also known as delayed-type hypersensitivity. This type of reaction is mediated by T lymphocytes rather than antibodies. Upon first exposure to an allergen, such as poison ivy or certain metals, the immune system sensitizes the T cells. On subsequent exposures to the same allergen, these sensitized T cells mount an inflammatory response, leading to symptoms such as redness, swelling, and itching at the site of contact.

The timing associated with Type IV reactions is key; they typically take 24 to 48 hours to develop, hence the term "delayed." This contrasts with other hypersensitivity types, such as Type I, which involves immediate reactions mediated by IgE antibodies, or Type II and Type III, which are associated with antibody-mediated responses and complement activation. Understanding the mechanism of Type IV hypersensitivity is crucial for diagnosing and managing conditions like contact dermatitis effectively. This knowledge enables healthcare providers to identify triggers and recommend appropriate avoidance strategies and treatments.