Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives or swollen airways. In some people, a food allergy can cause severe symptoms or even a life-threatening reaction known as anaphylaxis.
Food allergy affects an estimated 8% of children under age 5 and up to 4% of adults. While there’s no cure, some children outgrow their food allergies as they get older.
It’s easy to confuse a food allergy with a much more common reaction known as food intolerance. While bothersome, food intolerance is a less serious condition that does not involve the immune system.
An allergic reaction happens when the immune system reacts to a substance called an allergen. In food allergy caused by certain protein found in food, which for most people, is harmless. Why the immune system reacts in this way is not fully understood.
Not all reactions to foods are due to allergy. They may be due to other conditions including food intolerance (e.g. gluten or lactose), food poisoning (from bacterial or toxin contamination) or simply other illnesses that have similar symptoms.
Food allergies can be divided into two main types which are called IgE mediated (immediate) and non-IgE mediated allergy (delayed). More information on these types of food allergies can be found in our food allergy Factsheets.
Food allergies in children are often outgrown, although some persist into adulthood. Persistent food allergies include those to peanuts, tree nuts and sesame. It is possible to develop an allergy to food for the first time as an adult, and occasionally even to foods that have been eaten before without any problems.
Common culprits of food allergy include eight types of foods responsible for causing 90% of allergic reactions. These include cow’s milk, egg, fish, peanuts, shellfish, tree nuts, soya and wheat. However, it is possible that any food has the potential to cause an allergic reaction.
The most common food allergens are:
Going to the supermarket takes on a whole new meaning when you are avoiding common foods. You need to learn to read food labels and prepare more foods from scratch that you may have before. And every time you buy, you will need to read every label every time – manufacturers change their ingredients or processing aids from time to time. You will need to carefully check the ingredients list on food items and avoid foods which contain any of the ingredients causing allergy or food intolerance
Most allergic reactions are mild and resolve on their own, or after taking allergy medication (eg antihistamine). The most severe type of allergic reaction involves a person’s breathing and/or circulation and is called anaphylaxis which can be life threatening requiring urgent medical attention and treatment, but is rare.
For some people, an allergic reaction to a particular food may be uncomfortable but not severe. For other people, an allergic food reaction can be frightening and even life-threatening. Food allergy symptoms usually develop within a few minutes to 2 hours after eating the offending food. Rarely, symptoms may be delayed for several hours. Delayed allergic reactions affecting the digestive system and skin can occur up to 48 hours later and may be caused by Non IgE mediated allergy or intolerance.
The most common food allergy signs and symptoms include:
In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening signs and symptoms, including:
Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or even death.
Reasons for the increase in prevalence of food allergy are not known. There is a genetic component, with children of parents with allergies at higher risk, but it is generally acknowledged that environmental factors associated with a westernized life-style are driving this epidemic. Factors being investigated include ‘the hygiene hypothesis’; lifestyle changes leading to lack of Vitamin D; dietary changes; pollutants; and the effect of stress on the immune system