NHS Choices recommends antihistamines for mild to moderate food allergy reactions, and adrenaline for a severe reaction or anaphylaxis.⁴

In anaphylaxis, the immune response can affect the whole body, potentially within minutes, although anaphylaxis may occur after a few hours. It can arise from IgE cross-linking and high-affinity IgE receptors aggregating.

This triggers mast cells and basophils to quickly release mediators such as histamine, tryptase, carboxypeptidase A, and proteoglycans. This in turn activates phospholipase A2 (PLA2), cyclooxygenases and lipoxygenases, producing arachidonic acid metabolites, such as prostaglandins, leukotrienes, and platelet activating factor (PAF).²⁵

The presence of these various compounds triggers a range of physiological changes, including vasodilation, vascular permeability and cardiac changes by histamine, as well as bronchoconstriction and other pulmonary effects by prostaglandins, leukotrienes and PAF. Tumour necrosis factor activates neutrophils and other cell responses.²⁵

In addition to skin redness and urticaria, swelling of the mouth and throat makes it difficult to speak or swallow; there can be severe asthma, the heart rate may change, gastric pain, nausea and vomiting may occur, there may be a sudden drop in blood pressure, collapse and unconsciousness.²⁶

Treating anaphylaxis is best done as soon as possible using an adrenaline auto-injector to constrict blood vessels, relax smooth muscles in the lungs, stimulate the heart, and limit oro-mucosal swelling.²⁶