How are food allergies diagnosed?

If you see a doctor, they will first ask about your symptoms and what you had to eat or drink right before the symptoms started. If it's a regular problem, it can make sense to also keep a "food and symptom" diary for several days or weeks.

Like with other allergies, skin tests and blood tests can help to find out what is causing the symptoms. In the blood test, the doctor checks whether your body has produced certain antibodies (particularly IgE antibodies) to specific foods. In a skin prick test, solutions of potential food allergens are put on your forearm with enough space between them and your 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.

Doing an elimination diet can help in the diagnosis too. This involves avoiding the foods you think you might be allergic to for one to four weeks, and keeping track of any symptoms in a food diary.

To be more certain that you have a food allergy, though, a provocation test usually 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. This is done to intentionally trigger the symptoms. Depending on how severe the allergy is thought to be, the test is done in a doctor's practice or in a hospital in case urgent medical treatment is needed.

In children and teenagers, allergy tests are repeated regularly in order to check whether the food allergy has gone away again. Just how regularly will depend on the food that triggers the allergy: People with milk allergies, for instance, are tested more often than people who are allergic to peanuts or other nuts. This is because milk allergies often go away after a few years. Babies and toddlers only have blood tests, not skin tests.

Which tests aren't suitable for the diagnosis of food allergies?

Blood tests for other kinds of antibodies (known as IgG/IgG4 antibodies) are offered in some doctor's practices. But this test isn't currently recommended because it doesn't allow any clear conclusions to be drawn.

Other allergy tests are offered too, particularly by alternative practitioners. These tests include bioresonance, hair analysis, iridology (looking at the iris of your eye) and the ALCAT test – a blood test for signs of an inflammatory response. But these approaches aren't suitable for the diagnosis of allergies.

How are food allergies treated?

The main thing people can do to prevent allergic reactions is avoid the foods that cause them. How easy it is to do this will depend on the food you are trying to avoid. Professional dietary advice or patient education programs can help here: They provide information about how best to avoid the foods and what they can be replaced with. You learn how to recognize the foods when shopping, preparing meals and eating out. Dealing with anaphylactic reactions is also covered.

Milder symptoms are currently not usually treated with medication. There's hardly any research on how well medication works. But the few existing studies suggest that drugs known as H1 antihistamines can somewhat relieve acute symptoms affecting the skin. Medication is generally only used for the short-term treatment of more severe symptoms. Long-term treatment with medication is rarely offered.

Prebiotics and probiotics are often claimed to be effective in the treatment of food allergies. But there is no proof that this is true.

How are anaphylactic reactions treated?

In order to be able to treat anaphylactic reactions immediately, it's important to have an emergency kit nearby. These kits contain an adrenaline (epinephrine) injection, an antihistamine medication and an oral steroid medication in the form of a tablet or liquid. If the reaction is mild and you don't have breathing difficulties or circulation problems, you can take just the antihistamine and steroid medication at first. If the allergic reaction causes more serious problems such as breathing difficulties and circulation problems, it's important to inject the adrenaline into a muscle (preferably the thigh muscle) as soon as possible. You don't need to wait for the emergency services to do this. You can inject it yourself or have someone else inject it for you.

Can allergen-specific immunotherapy help?

Allergen-specific immunotherapy (desensitization) is a treatment option for other kinds of allergies, but not yet for food allergies. The substances needed for this kind of treatment haven't been approved for this purpose in Germany. A number of studies have looked into the effectiveness of immunotherapy in the treatment of various food allergies, such as allergies to peanuts or chicken eggs. But the studies found that people often had anaphylactic reactions to the treatment. So experts recommend only doing immunotherapy for food allergies if it is done as part of a study.

Which foods have to be replaced?

Some foods – such as nuts, fish or meat – can be removed from your diet without it having any significant effects on your health. Others might have to be replaced in order to prevent a lack of important nutrients such as proteins or calcium. One such example is cow's milk in children. Doctors should regularly check whether certain foods still need to be avoided, particularly in children.

Babies who can't have cow's milk can be given special "allergy-friendly" milk known as hydrolyzed milk. Soy milk isn't recommended for children under the age of one because some babies can't tolerate it.

How can you tell whether foods have allergy-triggers in them?

If food products contain any of the top 14 kinds of foods that can cause allergies, the manufacturers have a legal obligation to list them on the package labels:

1. Cereals containing gluten – such as wheat, rye, barley and oats

2. Crustaceans, e.g. shrimps, crabs and lobsters

3. Eggs

4. Fish

5. Peanuts

6. Soybeans

7. Milk

8. Nuts, e.g. almonds, hazelnuts and walnuts

9. Celery

10. Mustard

11. Sesame seeds

12. Sulfites

13. Lupin

14. Shellfish and mollusks (e.g. mussels, oysters and squid)

These foods and substances have to be clearly labeled on the package, for instance using a special font or background color. Unintentional traces of these foods don't have to be listed on the package label by law. But this is still done on many food packages.

People who sell unpackaged foods have to inform their customers about potential allergens too. Examples of such foods include bread and cake in a bakery, meals in a restaurant and meat from a butcher's. This information can be provided verbally (they can tell you), on paper (e.g. on the menu or in a leaflet) or digitally (e.g. on the business's website).

What can you do if you're exposed to food allergy triggers in your workplace?

Some people are affected by food allergies in their workplace. They usually come into contact with allergens by breathing them in or touching them. For instance, people who work in a bakery may develop a flour dust allergy, which can cause allergic rhinitis (e.g. sneezing and a runny or stuffy nose) and asthma symptoms. Some cooks get skin rashes when they repeatedly touch certain foods.

These effects of food allergies can be officially recognized as work-related diseases. In Germany, statutory accident insurers then cover the costs of certain measures. For instance, wearing protective clothing can reduce or prevent contact with allergens. Some allergens are easier to avoid than others, depending on the allergy and the type of work.

Sources

• Bundesministerium für Ernährung und Landwirtschaft (BMEL). Allergenkennzeichnung ist Pflicht. 2021.
• Chu DK, Wood RA, French S et al. Oral immunotherapy for peanut allergy (PACE): a systematic review and meta-analysis of efficacy and safety. Lancet 2019; 393(10187): 2222-2232. [PubMed: 31030987]
• 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). Allergieprävention (S3-Leitlinie, in Überarbeitung). AWMF-Registernr.: 061-016. 2021.
• Deutsche Gesellschaft für Allergologie und klinische Immunologie (DGAKI). Leitlinie zum Management IgE-vermittelter Nahrungsmittelallergien (S2k-Leitlinie). AWMF-Registernr.: 061-031. 2021.
• Dhami S, Panesar SS, Roberts G et al. Management of anaphylaxis: a systematic review. Allergy 2014; 69(2): 168-175. [PubMed: 24251536]
• 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]
• Romantsik O, Tosca MA, Zappettini S et al. Oral and sublingual immunotherapy for egg allergy. Cochrane Database Syst Rev 2018; (4): CD010638. [PMC free article: PMC6494514] [PubMed: 29676439]

• IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

  Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

  Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.