Most allergic reactions to food do not cause anaphylaxis. Severity depends on many different factors which we don’t fully understand at this time. These include: the amount of food eaten and what it was eaten in; what else was eaten at the same time; if the person has any other medical illnesses such as asthma or a cough/cold. Most children who have an accidental reaction after diagnosis do not have anaphylaxis but a more mild reaction.

We cannot predict who will have a life-threatening anaphylaxis reaction, which is why anyone with symptoms of anaphylaxis should receive immediate treatment with adrenaline by an injection into a muscle, to keep them safe.

We cannot predict which children with IgE-mediated food allergy might have anaphylaxis. Most people who have severe, life-threatening reactions have never had anaphylaxis before. Risk factors for severe reactions include poorly-controlled asthma and a delay in treating anaphylaxis with adrenaline.

When doctors decide if someone needs an adrenaline “pen”, they take into account a range of factors including the person’s previous reactions, if they have asthma or something else which might increase the risk of anaphylaxis, their age, the food(s) they are allergic to, and how easy it is to avoid that food.

Histamine is only one chemical released during an allergic reaction. Many different chemical signals are released in anaphylaxis: antihistamines takes around 30 minutes to start working, and will only ‘block’ one part of the reaction: they are not effective for severe reactions (anaphylaxis).

Adrenaline given by injection into the outer muscle of the mid-thigh (upper leg) is very safe. It starts to work within minutes, reducing swelling, relieving wheeze and improving blood pressure.

It also stops cells from releasing more inflammatory chemicals into the blood – so the earlier it is given during anaphylaxis, the better.