Which of the following antibiotics would MOST likely cause contact dermatitis?

• A. Penicillin
• B. Gentamicin
• C. Doxycycline
• D. Cephalexin

Answer: (B)

Contact dermatitis is a delayed-type (type IV) hypersensitivity reaction that can occur when a topical agent applied to the skin or eyelids acts as an allergen. The immune system becomes sensitized to the substance, and re-exposure triggers localized redness, itching, and swelling at the site.

Among these antibiotics, gentamicin is the one most commonly associated with a localized allergic reaction on the eye area when used topically. Penicillin, doxycycline, and cephalexin are more often linked to systemic allergic reactions or non-localized skin rashes rather than a pronounced contact dermatitis from ophthalmic use. Therefore gentamicin best fits the scenario of causing contact dermatitis.