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Why can improperly refrigerated fish cause histamine fish poisoning?

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antihistamines, including Benadryl — antihistamine Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H₁ receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.

Improperly refrigerated fish can cause histamine fish poisoning, also known as scombroid poisoning, because of the way bacteria interact with the fish's flesh.

When fish such as tuna, mackerel, skipjack, or mahi-mahi are not kept at proper temperatures, bacteria begin to break down the fish tissue. During this process, the bacteria act upon histidine—an amino acid naturally present in the fish protein—and convert it into high levels of histamine.12

Consuming fish contaminated with these elevated levels of histamine triggers an allergic-like reaction in humans. Symptoms typically include facial flushing, headache, nausea, vomiting, and itchiness. While these symptoms are often treated with antihistamines that block histamine receptors, the most effective way to prevent this illness is to ensure that susceptible fish are handled and stored at appropriate, cold temperatures to inhibit bacterial growth.12