Did you ever have a bad reaction to something you ate? Did you suspect it is because you could be allergic to certain foods? Food allergies affect 2%-4% of children and 2%-2.5% of adults. The most common causes are:
- For children: eggs, milk, peanuts, tree nuts
- For adults: shellfish, peanuts, tree nuts, fish, and eggs
In some cases, cross-reactivity happens. This means that if you are allergic to one type of food, like shrimp, then you could also be allergic to food related to it, like lobster.
What Happens During an Allergic Reaction?
An allergic reaction to food occurs because your body’s immune system identifies a particular food (or food protein) as harmful and, in response, creates antibodies called immunoglobulin E (or IgE for short). IgE antibodies attach to mast cells, which are found in places where allergic reactions are common—like the nose, throat, lungs, skin, and gastrointestinal (GI) tract.
IgE also prompts cells to release a chemical called histamine. Histamine causes symptoms like difficulty breathing, swelling, hives, and itching. It can also trigger an asthma attack. In severe cases, your body can go into anaphylactic shock —when you have trouble breathing and your blood pressure drops. If not treated quickly, this condition can be life-threatening. That is why it is so important for your doctor to determine if you have a food allergy.
How Does a Food Allergy Differ From a Food Intolerance?
Food allergy is sometimes confused with food intolerance because both conditions can cause GI problems—like gurgling stomach, stomach cramps and pain, nausea, and vomiting. Food intolerance, which is more common, means that you are sensitive to a food (or chemicals within the food) and you have an abnormal reaction to it. It may be difficult to determine which food is responsible for the reaction because sometimes the symptoms take time to appear.
Some of examples of food intolerance include:
- Food poisoning —If you eat contaminated meat, for example, this could trigger a reaction that is similar to a food allergy. But, really, your body is responding to the substances, like bacteria and toxins, in the food.
- Histamine toxicity—Histamine is found in our bodies, but it is also found in some foods. For example, fish that has spoiled, especially mackerel, can have high levels of histamine, which your body then reacts to.
- Lactose intolerance —This condition occurs when your body cannot digest lactose, a sugar in milk and other dairy products. Symptoms involve the GI tract (such as nausea, cramping, bloating, gas, and diarrhea).
- Food additives—You can also react to ingredients that are added to food to preserve it or make it taste better. The flavor enhancer monosodium glutamate (MSG), common in Chinese food, can cause flushing, headache, and chest discomfort. Sulfite, a preservative, can trigger an asthma attack in susceptible people.
- Gluten intolerance—This is linked to celiac disease, an autoimmune disease of the digestive tract. If you have gluten intolerance, the small intestine is damaged when you eat gluten, which is a protein in wheat, rye, and barley.
Other conditions can also trigger symptoms that resemble a food allergy. Peptic ulcers, for example, can cause nausea, vomiting, and bloating. Additionally, some people have a psychological reaction to food, which resembles a food allergy. If you ate something a long time ago and had a bad experience, you may be convinced that if you were to eat that particular food again, then the same reaction would occur.
How Are Food Allergies Diagnosed?
You will most likely be referred to a doctor who specializes in allergies, either an allergist or an immunologist. The doctor will ask detailed questions about your food reaction, such as when the reaction occurred, what you were eating, whether you took any allergy medication, how the food was prepared, among others. To help with the diagnosis, the doctor may ask you to keep a food diary for 1-2 weeks. In the diary, you carefully record what you eat, whether you had a reaction, and when the reaction occurred.
The main test used to diagnose a food allergy is the skin prick test. For this test, a small amount of extract of the food is placed on your skin and the skin is scratched. If a raised bump forms, this signals that you are allergic. A similar test involves using a needle to prick the skin with the food sample. These tests should only be done in a doctor’s office, since there is a chance of having severe reaction.
Blood tests, like ELISA, are used to determine if your body makes IgE antibodies in response to a particular food. These tests may be used to confirm skin test results.
With all tests, the results can vary. For example, a test can come back as positive, showing that you do make an antibody in response to milk protein. But, in your day-to-day life, you can drink milk and eat foods containing milk without having a problem. This is why your doctor considers your medical history and food diary, in addition to the test results, to make a diagnosis.
Other less commonly used techniques include elimination diets and food challenges. With elimination diets, you avoid the food that you may be allergic to and see if the symptoms disappear. If you eat the food again and the symptoms reappear, then the diagnosis is made. The problem with this technique, though, is that it cannot be used if you have a severe reaction.
Food challenges are helpful in proving that a food allergy has resolved. These challenges can be open or blind. In an open challenge, you eat increased amounts of a known allergen, and the doctor observes how you react. In a blind challenge, you eat food samples that are placed in capsules. You swallow one capsule at a time, without knowing which one is the suspected allergen. Your reaction is recorded. Both techniques must be done under a doctor’s care because of the risk of having a severe reaction.
What Is the Treatment for a Food Allergy?
Avoiding the food that causes the allergy is the main treatment, one that can be extremely challenging. You need to carefully read the list of ingredients when shopping and ask about meals when eating away from home. In some cases, even eating the tiniest amount of a particular food can cause you to have a reaction. The best approach is to be prepared for emergencies, especially if you are in danger of anaphylactic shock:
- Wear a medical alert bracelet.
- Carry an epinephrine shot (Epipen or Twinject). Be sure you know how to correctly use it.
- Call 911 if you have a reaction.
If your reaction is not as severe, your doctor may recommend that you take medications, such as antihistamines and corticosteroids. Removing the allergen after exposure is also helpful. According to the National Institute of Allergy and Infectious Diseases, if you have a peanut allergy and have touched food containing peanuts, washing your hands and cleaning counters with a household cleaner can remove the allergen.
For some people, an allergic reaction only happens when a certain food is eaten right before exercising. This seems to be triggered by the body temperature rising. Again, the treatment is to avoid the food; in this case, avoid eating two hours before exercising and always exercise with someone.
Another treatment still being studied is sublingual immunotherapy (SLIT). In SLIT, a small amount of the food you are allergic to is placed under your tongue. Done over a long period of time, the goal is to change how your immune system reacts to the food. Although promising, SLIT is not yet recommended.
Taking precautionary steps and being aware of allergens will help control your allergies. Call your doctor if you think you have a food allergy. If you need to find a specialist, the American Academy of Allergy Asthma & Immunology has a tool on its website to locate an allergist or immunologist in your area.
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