Introduction

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 is important to get the right diagnosis in order to get the right treatment – and avoid removing certain foods from your diet for no reason.

At a glance

• Food allergies can lead to reactions in and around your mouth, and cause problems with digestion and breathing.
• Common triggers of food allergies include nuts, eggs and seafood.
• If there are signs of an anaphylactic reaction, it’s important to call an ambulance right away.
• These allergies sometimes go away on their own after a few years.
• The most important thing is to avoid eating the foods that you're allergic to.

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:

• Reactions in the mouth and throat and on the skin: These are the most common symptoms. They involve itching and swelling, or rashes with reddened skin and hives.
• Gastrointestinal (stomach and bowel) problems: The typical symptoms are nausea, vomiting and diarrhea. They usually appear within half an hour of eating the food, or a few hours afterwards at the latest.
• Breathing problems: Signs include coughing, a hoarse voice or wheezing.

Foods can also trigger more severe anaphylactic reactions – possibly involving a sudden decrease in blood pressure and loss of consciousness. Swelling can affect the face and airways too, which may lead to breathing problems.

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 like celiac disease or lactose 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 too. So it’s important to see a doctor and get the right diagnosis.

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 and legumes: especially peanuts, walnuts and 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 between one and three different 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 allergies to milk, wheat or soy often “grow out of them” after a few years because their bodies learn to tolerate the allergens.

If 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 prick 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 a skin prick test, solutions of potential food allergens are put on the forearm with enough space between them, and the skin is gently pricked so the allergens can get into the skin. The skin is then observed to see whether it turns red or itchy and bumpy. In the blood test, the doctor checks whether the body has made certain antibodies (particularly IgE antibodies) to specific foods.

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 small amounts of 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.

Further information

When people are ill or need medical advice, they usually go to see their family doctor first. You can read about how to find the right doctor in our topic "Health care in Germany" – and our list of questions can help you to prepare for your appointment.

Sources

• Biedermann T, Heppt W, Renz H et al. Allergologie. Berlin: Springer; 2016.
• De Silva D, Geromi M, Panesar SS et al. Acute and long-term management of food allergy: systematic review. Allergy 2014; 69(2): 159-167. [PubMed: 24215577]
• Deutsche Gesellschaft für Allergologie und klinische Immunologie (DGAKI). Leitlinie zum Management IgE-vermittelter Nahrungsmittelallergien (S2k-Leitlinie). AWMF-Registernr.: 061-031. 2021.
• Institute for Quality and Efficiency in Health Care (IQWiG, Germany). AR101 (Peanut allergy): Dossier assessment; Commission A21-135. 2022.
• Kurowski K, Boxer RW. Food allergies: detection and management. Am Fam Physician 2008; 77(12): 1678-1686. [PubMed: 18619076]

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