Q: Why do we get hives in a food-allergic reaction? And will they always appear?
Dr. Sicherer: Hives, also called urticaria, develop when allergy cells in the skin release chemicals, including histamine, that cause localized swelling, redness and itching. The response looks like a series of mosquito bites, often across an expanse of skin, but various shapes and sizes can occur.
The allergy cells are armed with proteins made by the immune system, called IgE antibodies. The IgE antibodies act like antennae that can detect the food protein to which a person may be allergic. When the IgE comes in contact with the food protein, it alerts the cell to release the chemicals, including histamine.
Therefore, hives can occur from direct contact of the food with the deeper layer of the skin (like an allergy skin test) or from the proteins being absorbed in the gut, and then circulating in the blood and reaching the cells in the skin.
It is important to realize that while hives are classic sign of an allergic reaction, they do not always occur during allergic reactions or anaphylaxis.
Indeed, a severe reaction could include gut, breathing or circulation symptoms but no rash. In fact some fatal food-allergic reactions have occurred without hives, with a delay in treatment with epinephrine being attributed, in part, to not recognizing anaphylaxis because the victim did not have hives.
Dr. Scott Sicherer is Chief of the Division of Allergy and Immunology of the Jaffe Food Allergy Institute at the Icahn School of Medicine at Mount Sinai in New York. Together with Dr. Hemant Sharma, Associate Chief of the Division of Allergy and Immunology at Children’s National Medical Center in Washington, he writes “The Food Allergy Experts” column in the American Edition of Allergic Living magazine. Questions submitted below will be considered for answer in the magazine.