Introduction

Photo of a woman choosing a piece of cake at a café (PantherMedia / tonodiaz)

If someone keeps having the same reaction (e.g. nausea, a rash or feeling unwell) after eating certain foods, it may be logical to assume that they have a food allergy.

But food allergies are actually less common than many people believe: The symptoms are often caused by something else instead. It’s important to get the right diagnosis in order to get the right treatment – and avoid removing certain foods from your diet for no reason.

Symptoms

In food allergies, even small amounts of the food can be enough to trigger an allergic reaction. The symptoms can vary greatly and affect a number of different organs. In most cases the membranes lining the mouth and throat become swollen and itchy, or a red and itchy rash appears.

Sometimes the stomach and bowel are also affected, leading to symptoms such as nausea and diarrhea. Breathing problems may occur too. The symptoms usually appear within half an hour of eating the food, or within a few hours at the latest.

Foods can also lead to an anaphylactic reaction in the body (sometimes called “anaphylactic shock”), which can result in a sudden drop in blood pressure, unconsciousness, a skin rash, hives (nettle rash) and itching. Sometimes swelling occurs on the face and in the throat, which can make it difficult to breathe.

Different foods can cause different kinds of symptoms. For instance, fruits and vegetables tend to cause milder symptoms such as rashes, whereas nuts and shellfish often trigger severe allergic reactions.

The symptoms of food allergies can easily be mistaken for the symptoms of another medical condition or a food intolerance. Some foods contain additives and flavors such as monosodium glutamate, which can cause allergy-like symptoms. Gastrointestinal infections (“tummy bugs”) or IBS (irritable bowel syndrome) can result in similar digestive problems. So it’s important to see a doctor and get the right diagnosis.

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Causes and risk factors

In food allergies, the body’s immune system treats certain proteins in the food as if they were harmful, even though they are actually harmless.

Some people are more likely to develop allergies because allergies run in their family. People with certain food allergies might be allergic to pollen too – a phenomenon known as cross-reactivity. In other words, some people have both hay fever and a food allergy. This is because the protein in the food that they are allergic to is very similar to a protein in the pollen. When cross-reactions occur between pollen and a food, the pollen involved is usually birch pollen. People who are allergic to birch pollen are also more likely to be allergic to apples, celery, nuts or carrots, for instance.

But it still isn’t clear how food allergies develop in the first place. Typical triggers include:

  • Nuts: Peanuts, walnuts, hazelnuts
  • Chicken’s eggs, cow’s milk, soy, wheat
  • Celery, carrots, fruits containing pips (e.g. the small seeds in apples, pears, quinces), fruits containing a large “stone” (e.g. peaches, nectarines, plums)
  • Fish, seafood, meat

The most common food allergies in children are allergies to nuts, cow’s milk, soy, wheat and chicken’s eggs. Adults are usually allergic to nuts, soy, celery or seafood. Most people who have allergies are allergic to one, two or three foods.

Prevalence and outlook

About 4% of the population have food allergies. They can develop at any age. Depending on the age when they start, and what triggers them, allergies go on to develop in very different ways.

It is very difficult to predict whether and how a food allergy will change over time. The more severe the symptoms, and the stronger the reaction in allergy tests, the greater the likelihood that the allergy won’t go away. Children with milk, wheat or soy allergies often “grow out of them” after a few years because their bodies learn to tolerate the allergens.

If, on the other hand, an allergy first arises in adulthood, it is likely to stay. Such allergies typically include fish or seafood allergies. Nut allergies also tend to last a long time or never go away again.

About half of all children who have a food allergy also develop allergic asthma or allergic rhinitis (symptoms affecting the upper airways) later on in life.

Diagnosis

If it is thought that someone may have a food allergy, skin tests and blood tests can help to find out what is causing it. These tests check whether the immune system overreacts to certain triggers.

In the skin test, a solution containing a food protein is put on an area of skin that has been gently scraped, and the skin is observed in order to see whether it turns red or itchy. In the blood test, the doctor checks whether certain antibodies (particularly IgE antibodies) to specific foods have been produced.

These tests usually aren’t enough to find out for sure whether or not someone has a food allergy, though. A provocation test often has to be done too. Here, the person who is thought to have a food allergy eats the food in question under the supervision of a doctor.

Depending on the situation, a food and symptom diary or an elimination diet may help too.

Treatment

The main thing people can do to prevent allergic reactions is avoid the food that causes them.

Medication is generally only used in acute situations, if people have a more severe allergic reaction. It doesn’t tend to be used for the long-term treatment of food allergies.

Anaphylactic reactions are treated using emergency kits. These contain medications to reduce severe allergic reactions and prevent them from getting worse.

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Labels: Allergies, Cross reactivity, Food allergies, Food allergies, T78.4