There is a genetic factor in the development of allergic disease. If one parent has allergic disease, the estimated risk of a child to develop allergies is 48%; the child’s estimated risk grows to 70% if both parents have a history of allergies.

Our immune system is looking at millions of different things every day and trying to work out where it should focus its efforts. Sometimes it gets the focus wrong and decides to launch an all out attack on something that would never harm us - like a peanut or a tiny piece of pollen. Once your immune system has made up its mind that something is bad for us, it is very difficult to persuade it otherwise.

Even trace amounts of a food allergen can cause a reaction in some people with food allergies. Although ingestion is the primary cause of severe reactions, in some cases, skin contact or breathing in a food protein (e.g., steam from cooking shellfish) can cause symptoms.

Symptoms usually start as soon as a few minutes after eating a food and as long as two hours after. In some cases, after the first symptoms go away, a second wave of symptoms comes back one to four hours later (or sometimes even longer). This second wave is called a biphasic reaction. The risk of a biphasic reaction is why patients who have a severe reaction should stay at a hospital for four to six hours for observation.

Anyone who has a food allergy can have a severe allergic reaction to food. However, having asthma puts you at higher risk. Fatal outcomes of anaphylaxis include a disproportionate number of teens and young adults, possibly because they take more risks with their food allergies (eating dangerously and delaying treatment).

The most common way to treat an allergic reaction is to take antihistamines. These block histamine in the body, which is produced to protect the body from harm (i.e. from infection), and causes blood vessels to expand and skin to swell. It can be taken as a preventative measure or in response to an allergic reaction. Other treatments include steroids. These treatments are often taken in the form of tablets, a spray, or as a cream applied directly to the affected area (skin rash).

If you are with someone that is suffering from anaphylaxis (or anaphylactic shock), you need to act quickly. Get them to administer their epipen if they have one, or do it for them if they can't (as long as you know what to do). Call for emergency help (999). If you know what has caused the reaction, remove any traces of it if you can. For example, move potentially harmful food items out of the room and away from the individual or if possible, carefully remove the insect sting from the skin etc. Lie them down. If symptoms don't improve within a few minutes, you could administer another injection via an epipen, if available.