When there is too much histamine in fish, people should beware.

The Scombroid family of fish includes tuna and mackerel. When stored improperly, there can be too much histamine, which is not degraded by cooking. This causes symptoms of histamine excess, such as urticaria and all the usual culprits of unwellness.

The clinical diagnosis is based on history of multiple people being affected, rather than a single person with an allergy, as well as the redness of the presentation. Theoretically, the fish’s histamine can be measured. Histamine metabolites should show in the urine.

An antihistamine medication is the answer to this issue, such as the H1 antagonist diphenhydramine.

References

1. Sicari V, Patel P, Zabbo CP. Diphenhydramine. [Updated 2025 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526010/.
2. Liddiard, S., Nickson, C. and Nickson, S.L. (2024). Scombroid Poisoning. [online] Life in the Fast Lane • LITFL. Available at: https://litfl.com/scombroid-poisoning/.