Scombroid poisoning is a form of food poisoning. It happens when a person eats fish species containing high amounts of a chemical called histidine. Histidine is an amino acid that naturally occurs in fish. When people do not keep the fish in a refrigerator, bacteria break down the histidine and turn it into histamine. Histamine is responsible for the toxicity that causes scombroid poisoning, according to the American Academy of Allergy, Asthma & Immunology (AAAAI). When a person consumes large quantities of fish with histamine, they experience symptoms that resemble an allergic reaction, such as hives. However, it is not a true allergy to a particular fish, according to the National Capital Poison Center. The condition usually is not long-term or severe, according to the Food and Drug Administration (FDA) . Mild cases often disappear on their own without treatment, but antihistamine medications may help some people. A person experiencing severe symptoms, such as chest pain or b...