DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Penicillin allergy. Urticaria rash on the back of an 80-year-old man due to an allergic reaction to the antibiotic penicillin. Urticaria is an immune response to the presence of an allergen. The chemical histamine is released from skin cells, causing fluid to leak from tiny blood vessels into the skin tissues. Urticaria usually lasts a few hours, but can be relieved with antihistamine or corticosteriod drugs. Penicillin is used to treat infections by a wide range of bacteria, though some people are allergic to it.
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