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Food allergies: What you need to know and why

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Last updated date: 02.09.2025.

What are food allergies? A reaction to food that can be life-threatening. So take care to label leftovers in the fridge.

Food allergies can cause very severe reactions and symptoms may start very young. Babies can develop an allergy to milk, eggs or peanuts as early as six months old. But don’t let fear rule because there are ways to manage the condition if you get to know it inside out.

Food allergy numbers appear to have doubled between 2008 and 2018, according to a report in The Lancet by Paul J Turner et al, Time Trends in the Epidemiology of Food Allergy in England: An Observational Analysis of Clinical Practice Research Datalink data (September 2024).1 

You can be allergic to any food but some are more likely to trigger a reaction than others.2 This article will look at common food allergies and what causes them. Learn to recognise the symptoms and when you’re having a very severe allergic reaction (anaphylaxis). Not all food allergies work the same way and we’ll cover other types too, and other causes of symptoms after eating. Read how to get a diagnosis and how to manage life with food allergy afterwards, with our tips and information about treatment. 

Common food allergy triggers

There are 14 ingredients that commonly cause allergic reactions and must be highlighted on food packaging:2 Eggs, cow’s milk, fish, crustaceans, molluscs, peanuts, tree nuts, sesame seeds, cereals containing gluten, soybeans, celery and celeriac, mustard, lupin and sulphites.2 If companies can’t rule out cross-contamination, you might see a voluntary warning like “may contain traces of peanuts”. Food labelling laws also cover restaurants. 

Sulphites are preservatives often added to food like processed meats, pickles and sauces, dried fruit and juice, beer and wine.3 You may react to them if you already have allergic rhinitis or underlying asthma.

Gluten doesn’t generally cause a food allergy. But people with coeliac disease must avoid it completely. Eating less gluten may help if you have an intolerance to it.

What causes food allergies?

Food allergy starts in your immune system, which overreacts to proteins found in something you eat. The immune system’s job is to protect your body against bacteria or viruses that could make you unwell. Sometimes it gets it wrong and mistakes a particular food for a threat. The allergic reaction is your body trying to get rid of the food, or allergen, as fast as it can.4

How to read food labels

  • Triple check every food label: when you buy food, as you put it away at home and before you eat or serve it. It’s easy to miss something at a glance
  • Scan the packaging all over (not just the ingredients) for a “may contain…” warning and don’t take the risk if you find one
  • If you’re food shopping online look for a filter for allergies
  • Encourage even young kids to check labels for any food allergen. It makes great reading practice and soon becomes second nature
  • Tell the Food Standards Agency (FSA) if you get food allergy symptoms but there’s no allergen on the label
  • Sign up here for FSA email alerts about product recalls due to allergen contamination.

Step-by-step guide to developing food allergies

You don’t get a food allergy the first time you eat peanuts or shellfish or whatever your trigger is. Your immune system needs to build its defences first. It makes antibodies called Immunoglobulin E (IgE). Now you’re sensitised to that allergen. It doesn’t mean you’ll definitely develop a food allergy but you could.4

If you do, the IgE antibodies will fight back whenever you meet the allergen. They’ll tell other cells to release chemicals like histamine.4 Various fluids and white blood cells also travel to the site of the supposed attack to help. Pretty quickly you’ll feel the typical symptoms of an allergic reaction.

How quickly does an allergic reaction to food start?

Many people realise they’re having an allergic reaction in minutes or even seconds and usually within a couple of hours.5 One exception is a rare allergy to red meat that develops after a tick bite.6 The tick’s saliva can sensitise you to lamb, pork or beef. 6 Allergy symptoms tend to start 2 to 8 hours after a meal and can be severe.6

There’s another type of food allergy where the allergic reaction can start more slowly too – days later sometimes.  Read more about non IgE food allergies below.

Food allergy symptoms

Allergic reactions to food can range from mild to severe and these are some of the symptoms to look out for:5

  • Tingling or itching in the mouth
  • A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy but not raised
  • Swelling of the face, mouth, throat or other parts of the body
  • Difficulty swallowing
  • Wheezing or shortness of breath
  • Feeling dizzy and lightheaded
  • Feeling sick (nausea) or vomiting
  • Abdominal pain or diarrhoea
  • Hay fever-like symptoms such as sneezing or itchy eyes

The same person can react differently on different occasions. You may feel a bit unwell one time but need immediate medical treatment another. That’s why it’s important to see your GP if you suspect you may have a food allergy.

Woman reading the ingredients on food packaging at the supermarket – part of everyday life for someone with food allergies.

How to spot a severe allergic reaction to food

Have you heard of anaphylaxis (pronounced ana-fil-ax-is)? It’s a sudden and severe and often sudden allergic reaction that can be life-threatening.5 Having this type of reaction once increases the chance of it happening in the future,7 as does having poorly controlled asthma.7 Call 999 if you spot these warning signs on top of the food allergy symptoms above:7

  • Feeling lightheaded or faint
  • Difficulties with breathing, such as fast or shallow breathing
  • Wheezing
  • A fast heartbeat
  • Confusion and anxiety
  • Collapsing or losing consciousness

Some people can get these symptoms if they play sport after eating a particular food.8 It’s called food dependent exercise related anaphylaxis and luckily it’s fairly rare.8

Symptoms of Non IgE food allergies5,9

In this type of food allergies, protective white blood cells called T cells lead the allergic reaction instead. Symptoms are often delayed and affect the skin and digestion, with heartburn, indigestion, vomiting or diarrhoea common.

Non IgE food allergy symptoms are not usually severe but they can make children reluctant to eat. And that increases the risk of developing other health issues over time. Conditions include:

  • Food protein-induced allergic proctocolitis
  • Food protein enteropathy
  • Eosinophilic esophagitis
  • Food protein-induced enterocolitis syndrome

In mixed IgE and non-IgE mediated food allergies both mechanisms play a part. You may also get both types of symptoms.

Food allergy symptoms or cross-reaction?10

Certain fruit, vegetables, nuts and spices can make your lips itchy without being your main allergy trigger. The root cause is actually pollen allergy. That’s why this type of cross-reactivity is called oral allergy syndrome (OAS) or pollen food syndrome (PFS). And it affects around 2% of adults in this country, according to Allergy UK.

It happens because the food contains a protein very like the one in your problem pollen. Say grass pollen gives you hay fever. Well, you might get a mild local reaction in your lips, mouth, or throat when you eat tomatoes. Some foods linked to hay fever are also major causes of food allergy, such as almonds, hazelnuts, peanuts and soya.1 So tell your GP straightaway, just in case.

In rare cases people with dust mite allergy can react to shrimp, crab, lobster, clams and oysters for the same reason.11 Pork-cat syndrome is another rare cross-reaction. It usually happens quickly and has the same symptoms as IgE food allergies, so can be life-threatening.12

How to find out if you have food allergies?

Allergy testing is often the first step. That might be a skin prick test which involves putting a drop of liquid containing the allergen onto your arm, pricking the skin underneath it gently and checking for a reaction.5 Or you may need an allergy blood test to look for IgE antibodies.5 This will show if you’re sensitised to any food allergens. The GP will ask about your symptoms and family history of allergy13 before making a diagnosis. It can be helpful to keep food and symptom diary.

The process is different for non-IgE food allergies and for food intolerances.

Diagnosing delayed food allergies

Non-IgE food allergies are harder to diagnose – it’s a process.14 Your healthcare provider may ask for a stool sample and suggest an elimination diet to see what happens if you or your child stop eating a particular food.14 An internal examination with a camera (endoscopy) and biopsy might be necessary. 4 An oral food challenge can help confirm a diagnosis.14 It depends on the type of non-IgE allergy.14 

Diagnosing food intolerances

Intolerance is when your body struggles to digest a particular food.15 It’s nothing to do with the immune system, so allergy testing is no help.15 There are breath and blood tests for lactose intolerance.15 For other foods, the GP will probably suggest an elimination diet.15,16

Food intolerance can be distressing but isn’t usually serious.15 Symptoms tend to start more slowly than an allergic reaction.15 You may even find you can eat a small amount of the problem food without feeling unwell.16 In food allergies, even a tiny trace can cause a reaction.16 

Managing your food allergies

Don’t change your diet without talking to your doctor or allergist. They’ll work out a treatment plan with you. This is likely to involve avoiding your triggers as much as possible and treating symptoms with antihistamine or emergency adrenaline, depending on the severity, after accidental contact.

Depending on the allergy trigger, there may also be options for long-term relief.

Short-term and emergency symptom relief for food allergies

Antihistamine blocks the effect of the histamine your body releases as part of an allergic reaction.4 It’s only for mild to moderate food allergy symptoms.5 If your GP thinks you’re at risk of a severe reaction they’re likely to prescribe an adrenaline nasal spray or auto-injector.

Carry 2 adrenaline devices5,17,18 with you at all times. You could also think about wearing an allergy necklace or bracelet so people know how to help you in an emergency.

Long-term symptom relief for food allergies

Yes, there are treatments to reduce the risk of anaphylaxis from accidental contact with the food trigger. Ask your GP if either of these options might be suitable:

  • Food ladders:19 Most common with egg and milk, which is slowly introduced to build tolerance. Must be carried out under medical supervision in case of a severe reaction. Tends to be for kids who are more likely to grow out of their allergy. 
  • Oral immunotherapy:4 The only standardized food allergy immunotherapy at the moment is peanut. It’s available for eligible children from the age of and they still need to avoid their allergen afterwards.

6 ways to avoid your food allergy triggers

We’ve talked about reading food labels very carefully to help avoid common food allergy triggers and teaching kids to do the same. There are other good habits to get into that can help reduce the risk of having an allergic reaction both at home and on the go.

1. Check non-food products:  Skincare, cosmetics, petfood, vitamins, even modelling clay and finger paint can all include food allergens.

2. Be allergy aware when eating out: Get in touch with the restaurant beforehand to discuss exactly what you need from them not to have an allergic reaction. Help-yourself food counters like salad bars are best avoided. Other customers may have double-dipped the cutlery in something you’re allergic to.

3. Plan ahead when you travel: Tell the airline about your food allergies and order a special meal if you can. On trains and buses take your own food. Pack allergy medications in carry-on luggage in case of emergencies (plus spares in your suitcase). It’s sensible to carry both your prescription and a doctor’s letter; you may need to explain why you’re carrying meds. Breathing in food allergens is unlikely20 but you could pick them up on your hands from tables or armrests. So bring cleaning wipes. Translation cards or an app may help you identify allergens in a foreign country. 

4. Take care in the kitchen: Store food for someone with allergies on its own shelf and label containers. Clean surfaces, pots and pans, utensils and the microwave with a disposable wiper. Allergens can linger on sponges. Try always to eat at the table. And of course always wash your hands.

5. At school: Create an allergy action plan with your child’s school or care provider. And make sure your child knows all the forms of food and drink their allergen could appear in. Give them the confidence to ask adults about a food if they’re in any doubt. And to ask for help if they start feeling unwell – including with vomiting or diarrhoea.

6. Allergens exist in saliva too: Traces of peanut can linger in saliva for a few hours.21 So never share cutlery or drinking cups if you have food allergies. And at the risk of spoiling that first kiss, tell your date about your allergy first. 

The best general rule is to wash your hands with soap and water before eating or putting your hands near your face. And any time you think you may have been in contact with allergens.

For people with food allergies washing hands with soap and water is a must before eating. This little girl loves the bubbles.

Food allergy in children

Children may outgrow allergies to milk and other common early triggers such as eggs, cow’s milk and wheat. 22 But peanut, tree nut, fish and shellfish allergies are more likely to stay with you into adulthood.22 

One way to help prevent food allergies developing may be to introduce babies to peanuts and other trigger foods earlier than used to be the case.23 Allergy experts think starting from six months old might encourage the immune system to accept the allergens in later life.23 Talk to your GP or allergist first, especially if allergy runs in your family or your baby has eczema (atopic dermatitis). Both make it more likely a child could develop food allergies.13

Food allergies in adults

Around 6% of UK adults have a food allergy, according to the Patterns and Prevalence of Adult Food Allergy (PAFA) report, published by the Food Standards Agency in 2024.24 Some people will have been avoiding their trigger since early childhood. But about half of the allergies showed themselves for the first time in later adulthood.24 People sometimes mistakenly think they have food poisoning. But you know now that vomiting and diarrhoea can be symptoms of food allergy too.5 So why not speak to your GP just in case. 

The short version

Food allergies happen when your immune system overreacts to something harmless you’ve eaten. Symptoms can appear within minutes or hours and range from mild to so severe you need immediate treatment. Look out for itching or tingling in the mouth, hives, swelling of the face or throat, difficulty breathing, nausea, vomiting, diarrhea, dizziness, and be ready to dial 999.

Allergy testing will help your doctor pinpoint the cause and suggest a treatment plan. Common allergy triggers include eggs, milk, peanuts, tree nuts, fish, shellfish, soy, wheat (containing gluten), sesame seeds, celery, mustard, lupin and sulphites. You must avoid that food and carry emergency medication if prescribed. Children may outgrow some allergies like milk or eggs, but others like nuts often persist into adulthood.

References

1. Turner PJ, et al. Time trends in the epidemiology of food allergy in England: an observational analysis of Clinical Practice Research Datalink data. The Lancet Public Health. 2025;9(9):e664-e673.
https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(24)00163-4/fulltext

2. Food Standards Agency. Allergen guidance for food businesses. Geraadpleegd 8 augustus 2025.
https://www.food.gov.uk/business-guidance/allergen-guidance-for-food-businesses#allergens

3. Allergy UK. Sulphites and airway symptoms. Geraadpleegd 8 augustus 2025.
https://www.allergyuk.org/resources/sulphites-and-airway-symptoms-factsheet/

4. British Society for Immunology. Allergy briefing. Geraadpleegd 8 augustus 2025.
https://www.immunology.org/policy-and-public-affairs/briefings-and-position-statements/allergy

5. Allergy UK. Food allergy. Geraadpleegd 8 augustus 2025.
https://www.allergyuk.org/types-of-allergies/food-allergy/

6. UK Health Security Agency. Guidance: Alpha-gal Syndrome - The characteristics, symptoms, diagnosis and treatment of alpha-gal syndrome. Geraadpleegd 8 augustus 2025.
https://www.gov.uk/guidance/alpha-gal-syndrome

7. Muraro A, et al. EAACI guidelines: Anaphylaxis (2021 update). Allergy. 2022;77:357–377.
https://doi.org/10.1111/all.15032

8. Tam C-J, John RM. Food-Dependent Exercise-Induced Anaphylaxis: A Review. The Journal for Nurse Practitioners. 2017;13(5):313-321.
https://www.sciencedirect.com/science/article/pii/S1555415517300259

9. Calvani M, et al. Non-IgE- or Mixed IgE/Non-IgE-Mediated Gastrointestinal Food Allergies in the First Years of Life: Old and New Tools for Diagnosis. Nutrients. 2021;13(1):226.
https://www.mdpi.com/2072-6643/13/1/226

10. Allergy UK. Oral allergy syndrome (Pollen food syndrome). Geraadpleegd 8 augustus 2025.
https://www.allergyuk.org/resources/oral-allergy-syndrome-pollen-food-syndrome-factsheet/

11. Wong L, et al. Shellfish and House Dust Mite Allergies: Is the Link Tropomyosin?. Allergy Asthma Immunol Res. 2016;8(2):101-106.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4713872/

12. Abreu C, et al. Pork-cat syndrome?. Clin Transl Allergy. 2015;5(Suppl 3):P164.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4412402/

13. Chad Z. Allergies in children. Paediatr Child Health. 2001;6(8):555-566.
https://pmc.ncbi.nlm.nih.gov/articles/PMC2805592/

14. Labrosse R, et al. Non-IgE-Mediated Gastrointestinal Food Allergies in Children: An Update. Nutrients. 2020;12(7):2086.
https://www.mdpi.com/2072-6643/12/7/2086

15. NHS. Food intolerance. Geraadpleegd 11 augustus 2025.
https://www.nhs.uk/conditions/food-intolerance/

16. Allergy UK. Food intolerance. Geraadpleegd 11 augustus 2025.
https://www.allergyuk.org/resources/food-intolerance/

17. Neffy. Epinephrine nasal spray. Resources. Geraadpleegd 11 augustus 2025.
https://www.neffy.com/resources/

18. Gov.UK. MHRA approves adrenaline nasal spray - the first needle-free emergency treatment for anaphylaxis in the UK. Geraadpleegd 11 augustus 2025.
https://www.gov.uk/government/news/mhra-approves-adrenaline-nasal-spray-the-first-needle-free-emergency-treatment-for-anaphylaxis-in-the-uk

19. Hicks A, et al. The future of cow's milk allergy - milk ladders in IgE-mediated food allergy. Front Nutr. 2024;11:1371772.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10941844/

20. Turner P, Dowdall N. Flying with nut and other food allergies: unravelling fact from fiction. Archives of Disease in Childhood. 2025;110:334-340.
https://adc.bmj.com/content/110/5/334

21. Maloney JM, et al. Peanut allergen exposure through saliva: Assessment and interventions to reduce exposure. J Allergy Clin Immunol. 2006.
https://pubmed.ncbi.nlm.nih.gov/16950293/

22. Anaphylaxis UK. Will a child outgrow an allergy? Geraadpleegd 11 augustus 2025.
https://www.anaphylaxis.org.uk/fact-sheet/outgrowing-a-food-allergy/

23. NHS Food allergies in babies and young children. Geraadpleegd 2 september 2021.
https://www.nhs.uk/conditions/baby/weaning-and-feeding/food-allergies-in-babies-and-young-children/

24. Food Standards Agency. Patterns and Prevalence of Adult Food Allergy: Final report. Geraadpleegd 8 augustus 2025.
https://science.food.gov.uk/article/126077

GB-NPR-2500021 Sep. 2025

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