serum sickness in humans is a reaction to proteins in antiserum derived from a non-human animal source, occurring 5–10 days after exposure. it is a type of hypersensitivity, specifically immune complex hypersensitivity (type iii). the term serum sickness–like reaction (sslr) is occasionally used to refer to similar illnesses that arise from the introduction of certain non-protein substances, such as penicillin. it was first characterized by clemens von pirquet and béla schick in 1906.