Pathology · single question
Contact dermatitis is an example of which type of hypersensitivity?
Show answer and explanation
Correct answer: B. Type IV (T-cell mediated, delayed-type hypersensitivity)
- A. Type III involves circulating immune complexes — contact dermatitis is a local T-cell response in the skin.
- B. Correct. Contact dermatitis (e.g., from nickel jewelry, latex gloves, dental materials like eugenol) is Type IV DELAYED-TYPE hypersensitivity. CD4+ T helper cells (and CD8+ T cells) that were previously sensitized to the antigen become activated upon re-exposure, releasing cytokines that cause skin inflammation. The reaction occurs 24–72 hours after exposure.
- C. Type I reactions are immediate (minutes) and IgE-mediated — contact dermatitis is delayed (hours to days), ruling this out.
- D. Type II involves antibody-mediated cytotoxicity targeting cell surfaces — not relevant to contact dermatitis.