Food Allergies: Causes, symptoms, diagnosis, and treatments

What are food allergies?

A food allergy occurs when the immune system mistakenly identifies certain food proteins as harmful and reacts by releasing chemicals such as histamine. This immune response can trigger symptoms ranging from mild itching to severe, life-threatening anaphylaxis. Unlike food intolerances, food allergies involve the immune system and can occur even with very small amounts of the allergenic food.

According to the European Academy of Allergy and Clinical Immunology (EAACI), food allergies affect up to 10% of children and 2–3% of adults worldwide, with prevalence continuing to rise in many countries.

Food allergies symptoms

Symptoms of food allergies can vary from mild to severe and usually appear within minutes to two hours after eating the offending food. In some cases, delayed reactions can occur several hours later.

Common oral allergy syndrome include:

• Skin reactions: Hives, redness, itching, or swelling of the lips, face, or eyelids.
• Respiratory symptoms: Sneezing, coughing, nasal congestion, or difficulty breathing.
• Digestive symptoms: Nausea, vomiting, abdominal pain, or diarrhea.
• Cardiovascular symptoms: Dizziness, fainting, or a rapid drop in blood pressure.

In severe cases, food allergy can cause anaphylaxis, a medical emergency that requires emergency treatment with epinephrine. According to the World Allergy Organization (WAO), anaphylaxis is most often triggered by foods such as peanuts, tree nuts, shellfish, and milk in children.

Cause of food allergies

Food allergies develop when the immune system misidentifies harmless food proteins as harmful invaders. This abnormal immune response triggers the release of histamine and other inflammatory chemicals, leading to allergic symptoms. IgE-mediated allergies play a central role in this process. Once sensitized, even trace amounts of the allergenic food can provoke a reaction, sometimes within minutes.

Risk Factors

Several biological, genetic, and environmental factors increase a person’s likelihood of developing food allergies:

• Genetic predisposition: Family history is one of the strongest predictors. Children whose parents or siblings have allergies, asthma, or eczema are significantly more likely to develop food allergies. Certain genes related to immune regulation and skin barrier integrity (such as FLG mutations) have also been associated with a higher risk.
• Immune system imbalance: When regulatory immune cells fail to suppress allergic responses, the body becomes hypersensitive to harmless proteins. A weakened intestinal barrier allows allergens to cross more easily into the bloodstream, activating immune cells and triggering inflammation.
• Gut microbiota disruption: Early antibiotic use, cesarean delivery, or diets low in fiber can disrupt gut microbial balance. A less diverse microbiome has been linked to impaired immune tolerance, making the body more reactive to food antigens.
• Environmental influences: Urban pollution, reduced exposure to natural microbes, and Westernized lifestyles are thought to contribute to rising allergy rates. Children growing up in overly sterile environments may have fewer opportunities to develop natural immune tolerance.
• Early-life dietary patterns: Evidence suggests that early, supervised introduction of allergenic foods such as peanuts or eggs (around 4–6 months of age) may help prevent allergies by teaching the immune system to tolerate them. Conversely, delaying exposure during infancy can increase the risk of sensitization later in life.

8 common food allergies

Although any food can cause an allergic reaction, research shows that most cases are linked to a small group of foods known as the “Big Eight.” These foods are responsible for about 90% of all food allergies worldwide.

1. Milk: Cow’s milk allergy is most common in infants and young children. It usually causes skin rashes, digestive discomfort, or respiratory symptoms. Many children outgrow it by age five, but some remain allergic into adulthood.
2. Eggs: Egg allergy often appears early in life and is typically triggered by proteins in egg whites. Reactions can include hives, vomiting, or breathing problems. Heat-processed eggs are sometimes better tolerated due to protein denaturation.
3. Peanuts: One of the leading causes of severe allergic reactions, peanut allergy often persists for life. Even trace amounts can trigger anaphylaxis, requiring immediate epinephrine treatment.
4. Tree Nuts: Includes almonds, cashews, walnuts, pistachios, and hazelnuts. Reactions can be severe and cross-reactivity among different tree nuts is common, so strict avoidance is often advised.
5. Soy: Soy allergy can cause mild to moderate symptoms such as itching, stomach pain, or swelling. It’s more common in infants fed soy-based formulas but may improve with age.
6. Wheat: Triggered by proteins like gluten, wheat allergy may lead to hives, digestive symptoms, or asthma-like reactions. It differs from celiac disease, which involves an autoimmune response.
7. Fish: Fish allergy often develops in adults and tends to be lifelong. Even vapors from cooking fish can cause reactions in highly sensitive individuals.
8. Shellfish: Shellfish (shrimp, crab, lobster) is one of the most frequent causes of food-induced anaphylaxis in adults. Unlike other allergies, shellfish allergy rarely resolves and usually requires lifelong avoidance.

Other types of food allergies

Not all food allergies are IgE-mediated. Some are non-IgE-mediated, which mainly cause chronic inflammation in the digestive tract rather than immediate allergic reactions.

Eosinophilic Esophagitis (EoE)

A chronic inflammatory condition of the esophagus triggered by immune reactions to food proteins such as milk, wheat, soy, or eggs. It can cause difficulty swallowing, chest pain, vomiting, or food impaction, and is diagnosed through endoscopy and biopsy.

Food Protein-Induced Proctitis (FPIP)

Usually occurs in infants reacting to cow’s milk or soy protein. It causes mild rectal bleeding or mucus in the stool while the baby remains otherwise healthy. Symptoms typically resolve once the triggering food is removed and rarely persist beyond the first year of life.

Diagnosis and tests

Diagnosing food allergies involves combining medical history, physical examination, and specific allergy tests. Because symptoms may mimic other conditions, evaluation by an allergist is essential. Testing should always be guided by a detailed clinical history.

• Medical history and physical Exam: Doctors assess when and how symptoms appear, what foods are involved, and examine physical signs like hives or swelling to identify possible allergens.
• Skin prick test (SPT): A small drop of allergen is placed on the skin and lightly pricked. Redness or swelling suggests sensitization, but results must be interpreted with clinical context.
• Specific IgE blood Test: Measures allergen-specific IgE antibodies to detect immune responses. Useful when skin testing isn’t possible, though false positives can occur.
• Oral food challenge (OFC): The gold standard for diagnosis. The patient eats small, increasing doses of the suspected food under medical supervision to confirm an allergy.
• Elimination diet: Temporarily avoiding suspected foods and reintroducing them later helps confirm triggers but should be done with medical guidance.

Food allergies treatments

There is currently no permanent cure for food allergies, but symptoms can be managed effectively through avoidance, emergency preparedness, and, in some cases, immunotherapy. The main goal of treatment is to prevent allergic reactions and ensure patients know how to act quickly if they occur.

Prevention

Preventing food allergies aims to support immune tolerance from early life and minimize triggers that increase sensitivity. Below are effective strategies backed by current research:

• Early introduction of allergenic foods: Introducing allergenic foods like peanuts or eggs between 4–6 months of age may help prevent allergies, particularly in children with a family history of atopy. Early, supervised exposure helps the immune system learn to tolerate these foods rather than react to them.
• Breastfeeding and balanced nutrition: Exclusive breastfeeding for the first 4–6 months supports immune development and gut health. For both mother and child, maintaining a varied, nutrient-rich diet encourages tolerance to diverse food proteins.
• Healthy gut and microbiome support: A balanced gut microbiome is crucial for immune regulation. Limiting unnecessary antibiotic use, eating probiotic-rich foods, and maintaining a fiber-rich diet can help reduce allergy susceptibility.
• Gradual food diversification: Introducing a wide range of foods during infancy—not just common allergens—helps train the immune system to distinguish between harmful and harmless proteins. This may reduce the likelihood of developing new food allergies later in life.
• Hygiene and environmental balance: Overly sterile environments may limit exposure to helpful microbes that train the immune system. Allowing moderate outdoor play and contact with natural environments supports immune balance and reduces allergy risk.
• Monitoring and early consultation: For children with eczema, asthma, or a family history of allergies, early consultation with a pediatrician or allergist is key. They can provide personalized advice on timing and method of introducing allergenic foods safely