OVERVIEW

What is a food allergy?

A food allergy refers to a specific immune response triggered by antigenic substances in food after ingestion, which can cause tissue damage, physiological dysfunction, and a range of clinical symptoms^[1].

The prevalence of food allergies has increased significantly in recent years, with infants, young children, and children experiencing higher rates than adults. However, individual incidence tends to decrease with age.

What are the types of food allergies?

• Classification by affected organs^[2]
  Examples include allergic rhinitis, allergic dermatitis, and allergic enteritis.

• Classification by onset time
  Based on the time between ingestion and symptom onset, food allergies can be divided into immediate-type and delayed-type reactions.
  

Who is more likely to develop food allergies?

Infants, young children, and children.

While food allergies can occur at any age, infants and children are most susceptible, with significantly higher incidence rates than adults. The peak period for food allergies is between 4 to 6 months of age^[1].

SYMPTOMS

What are the common manifestations and symptoms of food allergies?

The specific symptoms and severity of food allergies are influenced by the amount of allergen ingested and the sensitivity of the individual^[1,3].

• Digestive system symptoms:
  Gastrointestinal symptoms mainly include nausea, vomiting, diarrhea, and abdominal pain. These symptoms lessen or disappear after the patient stops consuming the allergenic food. However, if the allergenic food is ingested again, the allergic reactions become more pronounced.
  Food allergies can also cause itching, numbness, swelling of the lips, and numbness or swelling of the tongue.
  In infants and young children, digestive symptoms mainly manifest as food-induced enterocolitis or malabsorption syndrome.

• Skin and mucosal symptoms: The primary manifestations include urticaria, angioedema or vasculitis, and atopic dermatitis, with the first two being the most common.

• Respiratory and ocular symptoms: These mainly include swollen and red eyelids, itchy eyes, tearing, nasal itching, sneezing, and runny nose.

• Cardiovascular symptoms: Chest pain, irregular heartbeat, low blood pressure, fainting, loss of consciousness, or even death.

CAUSES

What are the common allergens in food allergies?

Food allergens refer to the components in food that trigger allergic reactions in humans. They can be classified into the following types^[1,2]:

• Proteins: 90% of food allergens are proteins. Allergy-inducing proteins typically withstand food processing, heating, and cooking, as well as resist digestion in the gastrointestinal tract.
• Food additives: To improve food quality, color, flavor, and for preservation and processing purposes, various food additives are widely used. Allergies are commonly caused by spices and artificial colorings.
• Certain fermented foods: Such as beer and edible yeast.
• Genetically modified foods: Genetically modified organisms may contain genes from allergenic species or previously unused biological species. Genetic recombination can lead to the production of new proteins in host plants or animals, which may trigger allergic reactions in humans, such as genetically modified soybeans or tomatoes.

What are the pathways for food allergy induction?

Food allergens can enter the human body through various pathways to induce allergies^[1].

• Gastrointestinal route: Direct ingestion of food or processed products containing allergens.
• Respiratory route: Inhalation of allergens, such as flour causing asthma.
• Skin route: Skin contact with allergens triggering allergic reactions.
• Placental route: Maternal serum antibodies or large food antigens crossing the placenta can sensitize the fetus, leading to allergic reactions upon the first feeding after birth in rare cases.
• Breast milk route: Undigested antigens from the mother's diet passing through breast milk can cause allergies in infants who have never consumed the allergen.

What are the influencing factors of food allergies?

• Genetic factors:
  Genetics play a significant role in food allergies. If one or both parents have allergic diseases, their children are at a higher risk of developing food allergies.

• Individual factors^[1]:

  1. Selective immunoglobulin deficiencies;
  2. Altered mucosal permeability: Conditions like excessive alcohol consumption, inflammation, or ulcers can damage the intestinal mucosa, increasing its permeability and the chance of allergen invasion;
  3. Immaturity of the body: Infants have underdeveloped gastrointestinal digestion and immune functions, as well as delicate digestive mucosa and high vascular permeability, making them more susceptible to allergens entering the bloodstream;
  4. Physiological effects altering immune function. Antigen-antibody interactions release bioactive substances. Deficiencies in gastric acid, pepsin, or cholinesterase can enhance these reactions, increasing allergy risks.

• Food factors
  Certain proteins in food resist processing, heating, cooking, and digestion, making them more likely to cause allergies.

• Other factors

  1. Maternal consumption of allergenic foods during pregnancy increases the risk of food allergies in newborns;
  2. Premature and low-birth-weight infants, due to underdeveloped immune barriers, are more prone to food allergies;
  3. Early introduction of solid foods also raises the risk of food allergies.

DIAGNOSIS

What tests are needed to diagnose food allergies?

• Biochemical tests: Such as blood, urine, and stool tests, which help rule out non-allergic symptoms.
• Skin prick test: A skin prick test can help identify suspected food allergens, but a positive skin prick test alone cannot diagnose a food allergy.
• Serum antigen-specific IgE test: This test can help identify suspected food allergens, but a positive result also cannot confirm a food allergy.
• Oral food challenge (provocation test): This is the gold standard for diagnosing food allergies. For patients with corresponding medical history and laboratory test results, a positive provocation test can confirm a food allergy^[2,3].

TREATMENT

Which department should I visit for food allergies?

Patients should choose the corresponding department based on their earliest and most prominent symptoms. During diagnosis and treatment, doctors will determine whether the patient has a food allergy by reviewing medical history and conducting a series of relevant tests before proceeding with further treatment.

What to do if I develop rashes due to food allergies?

If rashes appear due to a food allergy, the first step is to stop consuming the allergenic food to avoid further exposure to the allergen. Then, seek medical attention promptly at the relevant hospital department. Under the guidance of a clinician, appropriate medication should be selected for symptomatic treatment based on the condition. During this period, maintain a light diet and avoid spicy or irritating foods to prevent worsening symptoms.

How should food allergies be treated?

• Avoidance therapy: Avoiding foods containing allergenic substances is the most effective way to prevent and treat food allergies.
• Deep processing of food: Deep processing can reduce or eliminate allergens in food. Heating can destroy allergens in raw foods—such as eggs, milk, and bananas—thereby reducing the likelihood of allergic reactions.
• Substitution therapy: Replace allergenic foods with alternatives. For example, those allergic to milk can opt for soy milk.
• Desensitization therapy: For severe food allergies where the allergenic food is nutritionally essential or difficult to avoid in daily life, patients can gradually increase their intake of the allergen to build tolerance. However, to prevent recurrence, excessive consumption of the adapted allergenic food should still be avoided^[1,3].
• Specific immunotherapy: Patients are injected with natural extracts of the allergen, with doses gradually increased to enhance tolerance and induce lasting immune tolerance, ultimately reducing allergic symptoms. However, clinical application of food allergy immunotherapy remains limited^[1,6].
• Probiotic therapy: Probiotics are live microorganisms that, when consumed in adequate amounts, benefit the host. Appropriate probiotic intake can alter gut microbiota and mucosal immunity, improving intestinal permeability and thus treating food allergies. For example, newborns allergic to milk who consume extensively hydrolyzed protein formula supplemented with Lactobacillus rhamnosus for six months may develop oral tolerance to milk allergens^[1,7].

Is there a cure for food allergies?

No.

Currently, there is no cure. Therefore, after clinical diagnosis or identifying allergens through medical history, strict avoidance of allergenic foods is essential.

DIET & LIFESTYLE

What are the common foods that cause food allergies?

There are over 160 types of foods that can trigger allergies, but the most common allergenic foods fall into the following 8 categories ^[1,5].

• Milk and dairy products: such as milk, cheese, etc. For details, see dairy allergy.
• Eggs and egg products: mainly chicken eggs. For details, see egg allergy.
• Peanuts and peanut products. For details, see nut allergy.
• Soybeans, other legumes, and various soy products.
• Grains and their products, such as wheat, barley, and oats. For details, see gluten allergy.
• Fish and fish products: including freshwater and saltwater fish. For details, see seafood allergy.
• Crustaceans and their products: such as shrimp, crab, clams, etc. For details, see seafood allergy.
• Tree nuts and their products: such as walnuts, sesame, almonds, cashews, etc. For details, see nut allergy.

In addition to these 8 common categories, some vegetables and fruits can also cause food allergies. Fruits that often trigger allergic reactions include apples, peaches, mangoes, and pineapples, while cucumbers, tomatoes, celery, and carrots may also cause food allergies.

What should people with food allergies pay attention to in daily life?

• Prevent food allergies at the source. Once the allergen is identified, strictly avoid consuming foods containing that substance.
• When purchasing food, carefully check the ingredient list on the nutrition label for raw materials, additives, and other information, and avoid buying foods containing allergens.
• When eliminating a specific allergenic food from the diet, replace it with alternative foods to compensate for the lost nutritional value and maintain a balanced diet.
• If a food allergy occurs, seek medical attention promptly and follow symptomatic treatment under the guidance of a clinician ^[1,3].

PREVENTION

How to Prevent Food Allergies?

Infants and young children are high-risk groups for food allergies.

Individuals with a personal or family history of allergies should pay attention to their diet during pregnancy and lactation, avoiding foods that commonly trigger allergies to reduce the risk in infants.

Additionally, to prevent food allergies in infants, complementary foods should not be introduced too early, and breastfeeding should be continued for at least 6 months^[1,4].