Scombroid poisoning is a foodborne illness that results from eating spoiled (decayed) fish. It is the second most common type of seafood poisoning, and is often mistaken for an allergic reaction. It typically occurs when people eat certain fish that have been inadequately preserved. Poisoning is due to a naturally occuring enzyme in the fish which when inappropriately stored or processed, is converted into histamine resulting in a reaction similar to that of an allergy.