Food Allergies: What You Need to Know

Author: Chioma Ezeobi, BPharm, Reviewed by: Dr Azuka Ezeike, MBBS, FWACS, FMCOG, MSc (PH)

Highlights

• A food allergy is when your immune system mistakes food or a substance in the food you eat as harmful.
• Food allergies have increased in the past years due to genetics, the environment, and modern lifestyle habits.
• Heredity, age, other allergic conditions, environment, and lifestyle are risk factors for food allergy.
• Common food allergies include milk, eggs, peanuts, tree nuts, fish, shellfish, wheat, soybeans, and sesame.
• Mild symptoms of food allergy are itching in the mouth, swollen face, lips, and eyes, vomiting, and nausea. 
• Swelling of the throat, low blood pressure and difficulty in breathing are severe and life-threatening symptoms.
• Food allergy is diagnosed using medical history, physical examination, skin prick tests, blood tests, elimination diets, and oral food challenges.

Introduction 

Do you know that difficulty in breathing or swelling of the face could be a sign of a food allergy?Your body is made up of natural soldiers called the immune system that protects you from anything harmful, like germs and bacteria, in the body, to keep you healthy [1].Food allergy is when these natural soldiers mistakenly identify food or a substance in the food as harmful and react to it.Food allergy has increased in the past 30 years due to inherited traits and the environment [2].

In a study in Cape Town, South Africa, a random group of people was tested, and about 2.5% were confirmed to have food allergies. Note that food intolerance is not the same as food allergy. Food intolerance is the inability of the digestive system to break down food or substances in the food [1].Food allergy is a reaction by the immune system to a food. It is more serious and can cause life-threatening symptoms like anaphylaxis [1]. Food allergies do not have a cure, the best prevention is to avoid them [1].

What causes food allergies?

When you eat certain foods, your immune system mistakes a protein in the food called allergens as harmful. Your immune system makes immunoglobulin E (IgE) antibodies to fight the allergen.The next time you eat that food, even in small quantities, the IgE recognises it and then tells the immune cell to release a chemical called histamine into the blood to fight it off. Histamine causes the symptoms of allergy, like itching and sneezing [1].

Risk factors of allergies 

Some factors increase the occurrence of allergies. They are:

• Heredity: If your parents or siblings have a food allergy, there is a high chance you will have it.
• Age: Most food allergies start in infancy because the baby’s immune system is not yet well-developed. However, some food allergies can begin in adulthood [2].
• Other allergic conditions: Having one allergy, like eczema or asthma, increases the chance of also having a food allergy.
• Environment: Exposing a baby to smoking, formula feeding, or delivery through cesarean section can increase the risk of food allergy. Children born in colder climates may also be at high risk due to low levels of vitamin D [1,2].
• Dietary: Introducing allergy-causing foods late to children prevents them from developing tolerance to the food. Thus increasing the risk of being allergic to the food. Also, not breastfeeding a child may weaken their immune system, as breast milk contains antibodies that help build their immune system [1]. 
• Lifestyle: The hygiene hypothesis suggests that if growing children are not exposed to everyday germs, such as playing with toys and older siblings, it makes their immune system weak. This makes their body more likely to overreact to harmless things like food [1].

Common allergy-causing foods 

According to the Food and Drug Administration (FDA), the nine most common food allergens are:

• Cow’s milk: It is one of the most common food allergies in children. According to the Association of UK Dietitians, about 2%-3% of babies and young children are allergic to milk. Most milk allergies usually begin in childhood, but they often grow out of it by the time they start school [3]. 

If you have a milk allergy, avoid milk and milk products like:

• Ice cream.
• Cheese.
• Butter.

• Eggs: It is an allergy to a protein in eggs. These proteins are ovomucoid, ovalbumin, and ovotransferrin, found mainly in the egg white and alpha-livetin, found in small quantities in the yolk [4]. They are a common allergy in children, which they outgrow with time.

Children who have egg allergies can take baked eggs without reacting to them [3,4].If you have an egg allergy, avoid egg and egg-containing foods like:

• Pastries.
• Mayonnaise.
• Egg sauce.

• Peanut: Also known as groundnut, is an allergy to a protein in peanuts. It can cause a serious and life-threatening reaction. It can begin in childhood or adulthood, and only 22% of children outgrow it [3]’

If you’re allergic to peanuts, avoid peanut and peanut-containing food like:

• Peanut butter.
• Granola.

• Tree nuts: It is an allergy to some of the nuts and seeds from the trees, such as almonds, cashews and walnuts. It affects 1% of the population and is less likely to be outgrown [4].  It causes a severe reaction of anaphylaxis.

If you have a tree nut allergy, it increases your chances of having other tree nut allergies.Avoid tree nuts and products containing them, like: 

• Chocolates.
• Candy.
• Cereals.

• Fish: It is an allergy to a protein in finned fish called parvalbumin. Examples of finned fish are:

  • Salmon.
  • Cod.
  • Tuna.

Most fish allergies start in adulthood and are often not outgrown. About half of the people with fish allergies are allergic to other types of fish, so it is best to avoid all fish and fish-containing food [3,4].Examples are:

• Sardine.
• Seafood.

You can be allergic to fish and not be allergic to shellfish because they do not contain the same protein.

• Shellfish: It is an allergy to seafood that has a shell-like outer part or inner part. They are of two groups:

  •  Crustacean: Crab, lobster and shrimp.
  •  Molluscs: Squid, oyster and clam.

Shellfish allergy mostly begins in adulthood. It has a high rate in coastal Asian countries where shellfish are a major part of their diet [5]’Tropomyosin is the major protein causing shellfish allergy, although there are other proteins, like arginine kinase. An allergy to the crustacean group does not mean you will have an allergy to the mollusc group. It is best to avoid all shellfish in your diet because one may contaminate the other [4,6]. Example of shellfish-containing diet:

• Sushi.
• Hamburger.
• Cracker.

• Wheat: It is an allergy to a protein in wheat. It is more common in children, which they outgrow before adulthood [3].

Wheat allergy is not the same as celiac disease and gluten intolerance. They are a reaction to gluten, a protein found in wheat and other grains [3].To manage a wheat allergy, avoid wheat and food containing wheat, like:

• Bread.
• Pasta.
• Beer.

• Soybeans: It is a reaction to a protein found in soybeans. It is common in infants and children, which they outgrow with time [4].

A soybean allergy does not mean you will be allergic to other legumes [3].If you are allergic to soybeans, avoid soybeans and food containing soybeans, like:

• Soymilk.
• Infant formula.
• Tofu.

• Sesame: It is an allergy to a protein in sesame seeds. It affects children and adults, but it is most common in children [6]. The FDA recently added it as the ninth common allergen in 2023.

If you’re allergic to sesame seeds, you will most likely be allergic to peanuts and tree nuts [6].Avoid sesame and food containing sesame, like:

• Cracker.
• Bread.
• Marinades.

Note that apart from these nine, you can be allergic to other types of food.

Symptoms of food allergies 

Food allergy symptoms could be mild, moderate, or severe [3].Below are symptoms to look out for:

 Mild to moderate symptoms

• Hives (red, itchy, and raised areas on the skin).
• Swollen face, lips, or eyes.
• Itching in the mouth and throat.
• Stomach pain.
• Vomiting, nausea, diarrhoea.
• Eczema.

Severe symptoms

• Anaphylaxis: It includes the following
  • Difficulty in breathing.
  • Cough that lasts for a long time.
  • Wheezing.
  • Sneezing.
  • Nasal congestion.
  • Dizziness.
  • Hoarse voice.
  • Swelling and tightness in the throat.
  • Low blood pressure.
  • Fainting.

Diagnosis of food allergy

Food allergies are diagnosed through the following tests:

• Medical history: Your doctor will ask detailed questions about the food you ate, your symptoms after eating it, and your family history of allergies. This information will help the doctor identify the allergy-causing food.

• Physical examination: The doctor examines you for symptoms of food allergy. Symptoms such as hives, difficulty in breathing, and swelling of the lips.

• Skin prick test: A small amount of suspected allergy-causing food is placed on your skin. A doctor uses a needle to prick the skin surface where the food is placed to allow a small quantity of the food into the skin.

If you’re allergic to the food, you will develop a red, itchy, raised bump on the skin.

• Blood test: Your blood sample is taken to measure the amount of Immunoglobulin E (IgE) antibodies specific to a suspected allergy-causing food [7]. A high amount of IgE shows an allergy to the food.

• Food elimination test: Your doctor will ask you to avoid a suspected allergy-causing food in your diet for a few weeks. He monitors you to see if the symptoms will disappear. If it does, he will ask you to introduce the food into your diet again. If the symptoms come back, you have an allergy to the food.

• Oral challenge: You are fed a suspected food allergen under the supervision of a doctor to check if you will react to it. The quantity of the food is gradually increased to see if you will tolerate a whole serving.

How to manage food allergies

Food allergies cannot be cured, but can be effectively managed by following the steps outlined below.:

• Avoid eating food that you’re allergic to.
• Check food labels and restaurant menus to be sure they’re free from food you're allergic to.
• Let your family, friends, school teacher, and colleagues know about your food allergy.
• Your doctor may prescribe medication to treat the symptoms of your allergy [8]. They’re:
  • Antihistamine: for minor allergies.
  • Epinephrine auto-injector (EpiPen): for treatment of severe allergic symptoms.
• Always keep at least two doses of EpiPen with you if your doctor has prescribed them.
• Ensure you and your child’s carer know how to use their prescribed EpiPen.
• If everyone in your house is not avoiding allergy-containing food,
  • Use separate cooking utensils, space and store for your food.
  • Cook allergen-free foods first before cooking other foods.

Conclusion

Food allergies can range from mild to life-threatening. Identify your allergy, foods containing the allergens, and symptoms.With this knowledge, you can carefully manage your allergies or those of your loved ones and live a healthy and safe life.When in doubt, always consult your doctor and dietitian for an allergy food plan. Do not leave the house without your epinephrine auto-injector if it is prescribed for you.

Reference 

1. Mauro C, Caterina A, Carlo C, et al. Food allergy: an updated review on pathogenesis, diagnosis, prevention and management. [Internet]. 2020 Sep. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC8023067/ 

2. Eric C, Brick T, Kathryn B, et al.The natural history and risk factors for the development of food allergies in children and adults. [Internet]. 2024 Feb. 24(3):121–131: Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC10960768/#CR27

3. Bhavisha Y, Gerald W. Food Allergy: Common causes, diagnosis, and treatment. [Internet]. 2015 Oct. Available from: https://www.mayoclinicproceedings.org/article/S0025-6196(15)00592-3/fulltext

4. Olivia L, Kathleen Y, et al. Common food allergens and cross-reactivity. [Internet]. 2020 Sep. 2(1):17–21. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11250430/

5. Samanta S. Seafood-associated shellfish allergy: A comprehensive review. [Internet]. 2016 Aug. 45(6):504-30. Available from: https://pubmed.ncbi.nlm.nih.gov/27404324/

6. Kelsey K, Jeffrey M. A practical focus on sesame allergy and a brief review of other seed allergies. [Internet]. 2022 July. 4(2):151–157. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11250203/#sec3

7. American College of Allergy, Asthma & Immunology. Food allergy testing and diagnosis. [Internet]. 2025. Available from: https://acaai.org/allergies/testing-diagnosis/food-allergy-testing-and-diagnosis/

8. Eric M, Anne M. Food allergy management. [Internet]. 2020 Sep. 2(1):59–63. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11250183/

Disclaimer:
The information provided on this website is for general educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Published July 7, 2025