Food Allergies: Types, Symptoms, Testing, Treatment

Food Allergies: Types, Symptoms, Testing, Treatment


A food allergy occurs when the body’s immune system mistakenly identifies proteins in certain foods as a threat and triggers an allergic reaction. More than 170 foods can trigger allergic reactions. Eggs, milk, peanuts, tree nuts, fish, shellfish, soybeans, and sesame are among the most common food allergens.

Food allergy symptoms typically begin within minutes to two hours after consuming the allergen and can range from mild to life-threatening. Hives and digestive issues are some of the more common symptoms. 

Food allergies affect more than 20 million adults and children in the United States alone. While there is no cure for food allergies, careful management and avoidance of food allergens, along with medications for reducing allergy symptoms, can help people with food allergies live well. 

There are two broad categories of food allergies: immunoglobulin-E-mediated (IgE-mediated) and non-IgE-mediated. While all food allergies involve an immune system response, the types differ based on how the immune system responds and the chemicals it releases in response to allergen exposure. 

Immunoglobulin-E-mediated (IgE-mediated) 

IgE-mediated food allergy involves the immune system making immunoglobulin E (IgE) antibodies. These antibodies trigger the release of inflammatory immune chemicals like histamine, which causes allergy symptoms.

Allergic reactions to IgE-mediated food allergens can occur minutes to two hours after exposure and involve the skin, heart, lungs, mouth, eyes, gut, and brain.

Non-IgE-Mediated

Non-IgE-mediated food allergies involve other immune system components in the gut that play a role in allergic reactions. Symptoms of non-IgE-mediated food allergies may take longer to develop, sometimes up to three days after allergen exposure. They primarily affect the gastrointestinal (GI) system but may also involve the lungs or skin. 

Food allergy symptoms can range from mild to severe and potentially life-threatening. Symptoms typically develop within minutes to a few hours after ingesting the allergen. They affect multiple body systems, including the skin, brain, digestive, and respiratory systems. 

Possible symptoms include:

  • Skin rash or hives (red, itchy bumps) 
  • Flushed (red) skin
  • Itchy or tingling sensations in the mouth or nose
  • Runny nose 
  • Cough 
  • Wheezing (whistling noises when breathing) 
  • Abdominal cramping 
  • Vomiting 
  • Diarrhea 
  • Itchy, watery eyes 
  • Dizziness or lightheadedness 

Anaphylaxis Symptoms 

A food allergy can cause anaphylaxis, a severe life-threatening reaction. It may begin with mild symptoms that rapidly worsen after ingesting an allergen. Anaphylaxis is a medical emergency and requires immediate treatment. Symptoms include: 

  • Hives
  • Throat or chest tightness
  • Facial swelling, including the eyes, lips, mouth, and tongue
  • GI symptoms like abdominal pain, nausea, vomiting, or diarrhea 
  • Heart palpitations
  • Nasal congestion 
  • Difficulty breathing or swallowing
  • Hoarseness or slurred speech
  • Feeling anxious or a sense of doom 
  • Loss of consciousness (fainting)

Food allergies occur when the immune system mistakes certain food proteins as harmful, triggering an immune response. When you have a food allergy, touching, eating, or inhaling proteins in certain foods (allergens) causes your immune system to produce immunoglobulin E (IgE) antibodies. These antibodies bind to two types of immune cells: mast cells and basophils. 

Subsequent (later) ingestion or exposure to the same food allergen causes the allergen to bind to the IgE-bonded immune cells. The cells release large amounts of inflammatory chemicals like histamine that lead to allergy symptoms.

Non-IgE-mediated food allergies occur when the immune system releases inflammatory cells and proteins, such as T-cells and cytokines, that weaken the protective intestinal barrier and cause gut inflammation. Research suggests this gut inflammation causes allergies to certain food proteins in people with non-IgE-mediated food allergies, leading to GI symptoms like vomiting, diarrhea, and abdominal cramping. 

Researchers are still exploring why some people develop food allergies and what factors contribute to their development, but evidence suggests genetic and environmental factors play a role. 

Risk Factors

Certain risk factors increase the likelihood of developing food allergies, including: 

  • Family history: Having a family member, such as a parent or sibling, with allergies increases your risk. 
  • Sex: Food allergies that develop in childhood are more common in people assigned male at birth, and adult-onset allergies are more common in people assigned female at birth.
  • Allergic conditions: People with other allergic conditions, such as eczema and asthma, are more likely to develop food allergies. 
  • Gut microbiome changes: Environmental factors that change the gut microbiome may play a role in food allergy development. Overuse of antibiotics, sterile indoor environments, and eating a high-fat diet can contribute to gut microbiome changes and increase the risk of food allergies. 

Diagnosing a food allergy is a complex process that requires the expertise of an allergist-immunologist (allergist). These medical doctors diagnose and treat allergies, asthma, and other immune-related conditions.

The provider will thoroughly review your medical history and ask about your symptoms and potential trigger foods. This includes: 

  • Your diet 
  • What foods (if you know) trigger allergy symptoms
  • What symptoms you experience, how quickly they develop after eating the food(s), and how long they last 
  • Whether you develop allergy symptoms every time you eat the food
  • What treatments you use (if any) after developing allergy symptoms

Allergy Tests

Allergy tests can help identify potential food allergens. These tests include: 

  • Skin prick test: Your healthcare provider will prick the skin on your arm or back with a sterile probe and insert a tiny amount of food allergen. If you are allergic to the allergen(s), you will develop skin allergy symptoms within 15-30 minutes, such as itchiness or a wheal (small bump). 
  • Blood test: Blood tests measure the amount of IgE antibodies in your blood specific to the food(s) you may be allergic to. While IgE antibody blood tests can indicate a food allergy, they cannot predict the severity of allergic reactions if you eat the food. 
  • Elimination diet: If it isn’t clear which foods are causing allergies, your allergist may recommend an elimination diet. This involves keeping a daily food diary of the foods you eat, symptoms you experience, and medications you take. Your allergist may recommend avoiding specific foods for 1-3 weeks to see if your allergy symptoms decrease. They may suggest gradually reintroducing the food and monitoring symptoms.
  • Oral food challenge: This is the gold standard in food allergy diagnosis. It involves consuming gradually increasing amounts of the suspected food allergen under careful medical supervision to observe for allergic reactions. 

Once you have a food allergy diagnosis, your allergist will work with you to develop a treatment plan to prevent allergic reactions and reduce symptoms when they occur. Your treatment plan may include avoiding allergens and developing an emergency plan.

Allergen Avoidance

Strict avoidance of food allergens is the most effective way to prevent allergic reactions. This requires: 

  • Carefully reading food labels when grocery shopping
  • Paying close attention to ingredients when eating at restaurants
  • Being aware of potential allergens hidden within processed foods
  • Staying vigilant about cross-contact when preparing food or dining at restaurants

Cross-contact occurs when a food allergen comes into contact with other foods, utensils, or cooking services. 

Emergency Preparedness

Your allergist may suggest developing an anaphylaxis emergency action plan outlining the steps to take after exposure to a food allergen. Your plan may include instructions on recognizing anaphylaxis symptoms and administering epinephrine. 

People with food allergies should always carry an epinephrine auto-injector (EpiPen). This medication treats severe allergic reactions (anaphylaxis) when accidental exposure to an allergen occurs. Epinephrine comes in single-dose, pre-filled automatic injection devices and can be lifesaving when administered at the onset of allergy symptoms. 

Medications

Medications can help manage mild allergy symptoms after accidental exposure to an allergen. Antihistamines like Benadryl (diphenhydramine) and Zyrtec (cetirizine) block histamines, which may help reduce symptoms like hives, itching, and runny nose. 

Healthcare providers sometimes administer corticosteroids in the emergency room after a severe allergic reaction to reduce inflammation and prevent symptoms from recurring.  

Oral Immunotherapy

Food allergy oral immunotherapy involves gradually introducing increasing amounts of the food allergen under medical supervision. The goal is to desensitize the immune system and build a tolerance to the food, potentially reducing or eliminating the allergic response.

Palforzia (peanut oral allergen powder) is the only FDA-approved oral immunotherapy. It is currently only available for people with peanut allergies and may reduce the frequency and severity of allergy symptoms in case of accidental exposure.

Biologic Therapy 

Biologic therapy targets and blocks immunoglobin E (IgE), the antibodies that drive food allergy reactions. Xolair (omalizumab) is an injectable medication with FDA approval for adults and children with food allergies. One Xolair injection once every 2-4 weeks may help increase tolerance to allergens and lower the risk of allergic reactions. 

There is no known way to prevent food allergies in adulthood, but emerging evidence suggests that preventing them in infants and children may be possible.

  • Early introduction: Introducing potentially allergenic foods, such as peanuts and eggs, during infancy may help reduce the risk of developing allergies to these foods. Experts recommend introducing safe forms of peanut and other allergen foods when babies are ready for solid foods, usually at 4-6 months old. 
  • Breastfeeding: Some studies suggest that breastfeeding infants may protect against allergic conditions, including food allergies. 

People with food allergies are more likely to have or develop other conditions that share similar immune-related responses, including: 

  • Eczema (atopic dermatitis): This chronic skin condition causes dry, itchy, inflamed patches of skin. Up to 40% of people with eczema have one or more food allergies. 
  • Asthma: This chronic respiratory condition causes wheezing, coughing, and difficulty breathing. Having a food allergy can worsen asthma symptoms and increase the risk of severe asthma exacerbations (asthma attacks).
  • Allergic rhinitis (hay fever): Allergies to airborne allergens like pollen can co-exist with food allergies. While the allergens are different, both conditions involve an overactive immune response.
  • Eosinophilic esophagitis: A condition that develops when high amounts of white blood cells called eosinophils accumulate in the esophagus and cause inflammation, leading to difficulty swallowing, chest pain, and feeling like something is stuck in the throat. 

Navigating life with food allergies requires careful management and vigilance, but it doesn’t have to limit your quality of life. Most people with food allergies can lead full and active lives by avoiding food allergens and establishing an emergency plan in case of accidental exposure. 

Talk to your healthcare provider if stress and anxiety related to your food allergies affect your day-to-day life. Your provider can provide you with the information you need and find resources to help you manage life with a food allergy. 

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