Histamine is the chemical that is responsible for most allergy-related symptoms. It is usually stored inside cells called mast cells. When one is exposed to allergens that he or she has been previously sensitized to, (e.g., pollens, dust mites, molds, animals, certain foods), the preformed specific antibodies react with their proteins (i.e., antigens) which cause a release of histamine and other similar substances from the mast cells into the tissues of the body. These chemicals in turn trigger various symptoms such as itching, sneezing, wheezing, coughing, runny nose, watery eyes, nasal congestion, post-nasal drip, etc.
Fish is one of the most common foods that cause food allergies. Sensitive individuals may experience allergic reactions after consuming fish. The classic mechanism of this type of allergic reaction is caused by antigen-antibody interactions. However, there are some people who are not sensitized or allergic to fish but can experience similar symptoms after eating fish. In these individuals, the symptoms are brought on by a different mechanism.
Many types of fish naturally contain a chemical called histidine. When the fish are not properly stored and refrigerated, bacteria overgrowth occurs in and on the fish. These bacteria release an enzyme called histidine decarboxylase which converts the naturally occurring histidine in the fish to a chemical called histamine. The enzyme is resistant to freezing and heating and can persist even after the bacteria are eliminated by normal cooking techniques. The resulting high levels of histamine cause the same symptoms as an allergic reaction, but the underlying mechanism is a type of toxicity rather than a true allergy.
This condition used to be called scombroid fish poisoning, as fish belonging to Scombridae family (e.g., tuna, mackerel, marlin, swordfish) were originally implicated. Later, many other non-scombroid fish such as mahi-mahi, sardine, herring, anchovy and bluefish were also found to cause this condition. The preferred current terminology is called “acute histamine toxicity.”
The symptoms usually begin 30 minutes to 2 hours after eating the fish. The most common manifestations may include:
- Generalized itching
- Reddish rash over the neck, upper torso, and/or upper extremities
- Throbbing headache
- Nausea, vomiting, abdominal cramps, and/or diarrhea
- Palpitations and/or dizziness
- Anxiety and/or chest tightness
- Swelling of the face and/or the tongue
- Difficulty in breathing
The diagnosis is usually made from the patient’s history. The appearance of the fish is sometimes described as honeycombed. Some affected individuals also experience a sharp, metallic, bitter, and peppery taste while eating the fish. Laboratory tests are usually not helpful as histamine is rapidly degraded and cannot be detected in blood or urine samples within 1 to 2 hours after the onset of symptoms. The presence of a specific IgE antibody in the blood to the fish usually indicates an allergic reaction and not a toxic reaction due to the high levels of histamine. Clusters of individuals exhibiting similar symptoms after eating the same meal generally points more to histamine poisoning rather than an allergic reaction.
The treatment of this condition involves medications that focus on the relief of symptoms. Antihistamines [H-1 blockers (e.g., Benadryl, Claritin, Allegra, Zyrtec) along with H-2 blockers (e.g., Zantac, Tagamet)] are useful in relieving the itching and rash. Corticosteroids may be appropriate in certain more severe situations. Bronchospasm which may cause wheezing, shortness of breath, chest tightness, and/or coughing can be treated with albuterol inhalations. Rarely, some people may also need intravenous hydration. Fortunately, most cases of histamine toxicity are self-limited and the symptoms often resolve spontaneously within 6 to 8 hours.
The prevention of acute histamine toxicity requires proper and continuous refrigeration of fish until the time of cooking. This should prevent bacterial overgrowth and likewise the conversion of histidine to histamine.
The board certified allergists at Black and Kletz Allergy have 3 convenient locations [Washington, DC; McLean, VA (Tysons Corner, VA); Manassas, VA] in the Washington, DC metropolitan area. The allergy doctors have been trained in providing allergy care for both adults and children. They in fact have been diagnosing and treating adults and children with allergies for more than 50 years. They will promptly answer any questions you may have regarding food allergies, food sensitivities, food toxicities, and related disorders. The allergy specialists can also help you with other allergic conditions such as asthma, hives, swelling episodes, insect sting allergies, medication allergies, contact dermatitis, generalized itching, eczema, sinus disease, anaphylaxis, eosinophilic disorders, and immune disorders.
All 3 offices of Black & Kletz Allergy offer on-site parking. The Washington, DC and McLean, VA offices are Metro accessible and we offer a free shuttle that runs between our McLean office and the Spring Hill metro station on the silver line. Please call our office to schedule an appointment or alternatively, you may click Request an Appointment and we will respond within 24 hours by the next business day.