Sulfa alergy is the term which is widely used for describing the unfavorable drug reactions to sulfonamides which is the group of drugs that incorporate those drugs with or without antibiotic features. Sulfonamides were the first antibiotics that were used for treating various infections before the invention of penicillin.

The antibiotic grades of sulfonamides differ from the non-antibiotic sulfonamides in its chemical composition and pose to cause allergic reactions. Skin reactions are the most commonly noticed unfavorable reactions to sulfa medications which include: gentle rashes to life threatening Stevens-Johnson syndrome and toxic epidermal necrolysis. Hives and enhanced sensitivity to the sunlight may also be faced.

People with sulfa allergy may experience a type of hepatitus and kidney failure due to sulfa medications. Alergy to some typical sulfa drug increases the risk of reacting to the other sulfa drugs too.