Food allergies: what are they and how are they treated?

Food allergies affect around 3–8% of children and 1–3% of adults in the UK. It occurs when your body’s immune system overreacts to harmless substances (allergens) you ingest. 

Food allergy versus food intolerance

A food allergy is not the same as a food intolerance.

Many more people in the UK have a food intolerance but this does not involve the immune system, as with a food allergy.

Although the exact cause of a food intolerance is unknown, symptoms may be caused by reactions to chemicals present in your food or drink (eg caffeine), or by enzyme deficiencies (eg lactose intolerance).

Consequently, symptoms of a food intolerance, which can overlap with some of the symptoms of a food allergy, usually appear gradually over several hours and are not life-threatening.

In contrast, symptoms of a food allergy usually occur between a few minutes or up to an hour after exposure, and in some cases, can be fatal if left untreated.

Food allergy risk factors

Your risk of developing a food allergy is greater if you or your family have other atopic conditions, eg atopic eczema, asthma and hay fever. 

Infants with early-onset eczema (ie before six months) have a particularly high risk of developing a food allergy. This is because their body’s first interaction with potential food allergens is more likely to be through their damaged skin than through ingestion. This results in their immune system wrongly identifying the food substance as harmful and later, when ingested, may cause an allergic reaction to the food. 

Common food allergies

The most common food allergies in the UK are in response to eggs, cow’s milk, peanuts, tree nuts, fish, shellfish, wheat, soya and sesame.

Shellfish allergies tend to be more common in adults, while fish allergies tend to be more common in children.

Around one in five children with a peanut allergy will grow out of it and as adults, can eat peanuts without having an allergic reaction.

How to prevent food allergies in children

Exclusively breastfeeding infants for their first six months of life can help prevent or delay the onset of allergies, especially in families with a history of atopic conditions.

Early exposure to food allergens in infants at around four to six months but before 12 months may help prevent the development of food allergies. In infants with eczema in particular, the goal is to expose the infant to the food allergen via ingestion before they are exposed to it via their damaged skin.

This is because ingesting potential food allergens activates a process in your immune system that identifies and remembers that these substances are harmless.

Food allergy symptoms

If you suspect you have a food allergy you should see your GP. 

Symptoms usually start a few minutes after exposure to a food allergen but can take up to an hour to develop. 

Initial symptoms include tingling or an itchy feeling in your mouth, a scratchy throat and palate (roof of your mouth), and swollen lips. You may also develop hives (nettle rash), a swollen tongue and eyes, a runny, itchy nose, and gastrointestinal symptoms eg vomiting, diarrhoea, stomach cramps. 

In more severe cases, you may develop anaphylaxis, where in addition to the above symptoms, you experience difficulty breathing and a drop in your blood pressure, resulting in dizziness and light-headedness. You may also collapse and become unconscious. 

Anaphylaxis is a medical emergency and you should call 999. You should still go to A&E for observation even if you have used an adrenaline autoinjector to treat your anaphylaxis. This is because you may develop biphasic anaphylaxis, where your body goes into anaphylaxis again despite being previously treated and not being exposed to the allergen again. 

Treating food allergies

The most effective treatment is avoiding the triggers of your food allergy.

However, this is not as simple as just avoiding the specific food allergen. You also need to avoid any foods which might cross-react with this particular allergen ie food allergens that are similar enough to the known trigger of your food allergy to cause your immune system to overreact.

You should be cautious to avoid accidental exposure to the specific food allergen in cross-contaminated meals. It is, therefore, always important to check food labels and when eating out, declare your allergies.

You should also always carry an emergency kit containing an adrenaline injector, antihistamine medication and, if you have asthma, an inhaler.

In children with a peanut allergy, immunotherapy treatment is available. This is where the child is exposed to small but increasing doses of the peanut allergen slowly over time, until the body is trained not to react. This isn’t a cure but can help reduce the severity of their peanut allergy.