Food allergy

Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives or swollen airways. Food allergy affects an estimated 6 to 8 percent of children under age 3, and about 4 percent of adults. While there’s no cure, some children outgrow their food allergy as they get older. It’s easy to confuse a food allergy with a much more common reaction known as food intolerance. While bothersome, food intolerance is a less serious condition that does not involve the immune system.

Causes Food allergy

n a true food allergy, your immune system mistakenly identifies a specific food or a substance in food as a harmful substance. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE) antibodies to fight the culprit food or food substance (the allergen). The next time you eat even the smallest amount of that food, the IgE antibodies sense it and signal your immune system to release a chemical called histamine, as well as other chemicals, into your bloodstream.

These chemicals cause a range of allergic signs and symptoms. They are responsible for causing allergic responses that include dripping nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing, and even anaphylactic shock.

The majority of food allergies are triggered by certain proteins in:

  • Shellfish, such as shrimp, lobster and crab
  • Peanuts
  • Tree nuts, such as walnuts and pecans
  • Fish
  • Eggs

In children, food allergies are also commonly triggered by proteins in:

  • Eggs
  • Milk
  • Peanuts
  • Tree nuts

Chocolate, long thought by some parents to cause food allergies in children, rarely triggers a food allergy.

Food intolerance and other reactions
There are a number of reactions to food that cause similar symptoms to a food allergy. If you have digestive symptoms, chances are it’s not a true food allergy, but a food intolerance. Depending on the type of food intolerance you have, you may be able to eat small amounts of problem foods without a reaction. By contrast, if you have a true food allergy, even a tiny amount of food may trigger an allergic reaction. Because a food intolerance may involve some of the same signs and symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea — people often confuse the two.

One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself but to a substance or ingredient used in the preparation of the food.

Common conditions that can cause symptoms mistaken for a food allergy include:

  • Absence of an enzyme needed to fully digest a food. You may not have adequate amounts of some enzymes needed to digest certain foods. Insufficient quantities of the enzyme lactase, for example, reduces your ability to digest lactose, the main sugar in milk products. Lactose intolerance can cause bloating, cramping, diarrhea and excess gas.
  • Irritable bowel syndrome. Certain foods may trigger the signs and symptoms of irritable bowel syndrome. You may find that certain foods will cause cramping, constipation or diarrhea. Steer clear of these foods to avoid the symptoms.
  • Food poisoning. Sometimes food poisoning can mimic an allergic reaction. Some types of mushrooms and rhubarb can be toxic. Bacteria in spoiled tuna and other fish also can make a toxin that triggers harmful reactions.
  • Sensitivity to food additives. Some people have digestive reactions and other symptoms after eating certain food additives. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people. Other food additives that could trigger bad reactions include monosodium glutamate (MSG), artificial sweeteners and food colorings.
  • Recurring stress or psychological factors. Sometimes the mere thought of a food may make you sick. The reason is not fully understood.
  • Celiac disease. While celiac disease is sometimes referred to as a gluten allergy, it isn’t a true food allergy. Like a food allergy, it does involve an immune system response, but it’s a unique immune system reaction that’s more complex than a simple food allergy. This chronic digestive condition is triggered by eating gluten, a protein found in bread, pasta, cookies, and many other foods containing wheat, barley or rye. If you have celiac disease and eat foods containing gluten, an immune reaction occurs that causes damage to the surface of your small intestine and an inability to absorb certain nutrients. Symptoms of celiac disease include diarrhea, abdominal pain and bloating. In some cases, celiac disease causes malnutrition and nutrient deficiencies.

Food allergy symptoms

Food allergy symptoms usually develop within a few minutes to an hour after eating the offending food.

The most common food allergy symptoms include:

  • Tingling in the mouth
  • Hives, itching or eczema
  • Swelling of the lips, face, tongue and throat, or other parts of the body
  • Wheezing, nasal congestion or trouble breathing
  • Abdominal pain, diarrhea, nausea or vomiting
  • Dizziness, lightheadedness or fainting

Anaphylaxis
In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening symptoms, including:

  • Constriction and tightening of airways
  • A swollen throat or a lump in your throat that makes it difficult to breathe
  • Shock, with a severe drop in blood pressure
  • Rapid pulse
  • Dizziness, lightheadedness or loss of consciousness

Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or death.

Exercise-induced food allergy
Some people have an allergic reaction to a food triggered by exercise. As the body is stimulated by exercise, a person with an exercise-induced food allergy may feel itchy and lightheaded. In serious cases, it can cause reactions such as hives or anaphylaxis. Not eating for a couple of hours before exercising and avoiding certain foods may help prevent this problem.

Pollen-food allergy syndrome
In many people who have hay fever, fresh fruits and vegetables and certain nuts and spices can trigger an allergic reaction that causes the mouth to tingle or itch. In some people, pollen-food allergy syndrome — sometimes called oral allergy syndrome — can cause swelling of the throat or even anaphylaxis. This is an example of cross-reactivity. Proteins in fruits and vegetables cause the reaction because they’re similar to those allergy-causing proteins found in certain pollens. For example, if you’re allergic to ragweed, you may also react to melons; if you’re allergic to birch pollen, you may also react to apples. Cooking fruits and vegetables can help you avoid this reaction. Most cooked fruits and vegetables generally don’t cause cross-reactive oral allergy symptoms.

Complications of food allergy can include:

  • Anaphylaxis, a life-threatening allergic reaction.
  • Atopic dermatitis (eczema). About one in three people with atopic dermatitis also have a food allergy.
  • Migraines. Histamines, released by your immune system during an allergic reaction, have been shown to trigger migraines in some people.

Food allergy test

  • Skin test. A skin prick test can determine your reaction to particular foods. In this test, small amounts of suspected foods are placed on the skin of your forearm or back. Your skin is then pricked with a needle, to allow a tiny amount of the substance beneath your skin surface. If you’re allergic to a particular substance being tested, you develop a raised bump or reaction.
  • Blood test. A blood test can measure your immune system’s response to particular foods by checking the amount of allergy-type antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. For this test, a blood sample taken in your doctor’s office is sent to a medical laboratory, where different foods can be tested. However, these blood tests aren’t always accurate.

Food allergy treatments

For a minor allergic reaction, over-the-counter or prescribed antihistamines may help reduce symptoms. These drugs can be taken after exposure to an allergy-causing food to help relieve itching or hives. However, antihistamines can’t treat a severe allergic reaction.

For a severe allergic reaction, you may need an emergency injection of epinephrine and a trip to the emergency room. Many people with allergies carry an autoinjector (EpiPen, EpiPen Jr or Twinject). This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh.

While there’s ongoing research to find better treatments to reduce food allergy symptoms and prevent allergy attacks, there isn’t any proven treatment that can prevent or completely relieve symptoms. Unfortunately allergy shots (immunotherapy), a series of injections used to reduce the effect of other allergies such as hay fever, aren’t effective for treating food allergies.

Food allergy Prevention

While there’s ongoing research to find better treatments to reduce food allergy symptoms and prevent allergy attacks, there isn’t any proven treatment that can prevent or completely relieve symptoms. Unfortunately allergy shots (immunotherapy), a series of injections used to reduce the effect of other allergies such as hay fever, aren’t effective for treating food allergies.

The key treatment is to do your best to avoid the food in question, and work with your doctor to identify what steps you can take to relieve your symptoms and how to spot and respond to a severe reaction.