What is a 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. In some people, a food allergy can
cause severe symptoms or even a life-threatening reaction known as anaphylaxis.

Food allergy affects an estimated 6 to 8 percent of children under age 5, and about 3 to 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.

Symptoms

For some people, an allergic reaction to a particular food may be uncomfortable but not severe. For other people, an allergic food
reaction can be frightening and even life-threatening. Food allergy symptoms usually develop within a few minutes to two hours
after eating the offending food. Food allergies can occur even the first time you eat a food.

The most common food allergy symptoms include:


Tingling or itching 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 the sensation of 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. Eating certain foods may cause you to feel itchy and
lightheaded soon after you start exercising. In serious cases, an exercise-induced food allergy 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.

Causes

When you have a food allergy, your immune system mistakenly identifies a specific food or a substance in food as something
harmful. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE) antibodies to neutralize 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 allergy 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 commonly triggered by proteins in:

Eggs
Milk
Peanuts
Tree nuts
Wheat
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. 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 may 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.

Food poisoning. Sometimes food poisoning can mimic an allergic reaction. 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 severe 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, leading to an inability to absorb certain nutrients.


Western Medicine Treatment

The only way to avoid an allergic reaction is to avoid the foods that cause signs and symptoms. However, despite your best efforts,
you may come into contact with a food that causes a reaction.

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 epinephrine autoinjector (EpiPen, EpiPen Jr, Twinject). This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh. If your doctor has prescribed an epinephrine autoinjector:


Carry it with you at all times. It may be a good idea to keep an extra autoinjector in your car or in your desk at work.

Always be sure to replace epinephrine before its expiration date, or it may not work properly.

Be sure you know how to use the autoinjector. Also, make sure the people closest to you know how to administer the drug — if they're with you in an anaphylactic emergency, they could save your life.


Experimental treatments

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. Two treatments
that have shown some promise are:


Anti-IgE therapy. The medication omalizumab (Xolair) interferes with the body's ability to use IgE. The drug is currently being studied for treatment of allergic asthma and food allergies. However, this treatment is still considered experimental and more research needs to be done on the drug's long-term safety. It has been associated with a potential increased risk of anaphylaxis.

Oral immunotherapy. Researchers have been studying the use of oral immunotherapy (OIT) as a treatment for food allergy. Small doses of the food you're allergic to are swallowed or placed under your tongue (sublingual). The dose of the allergy-provoking food is gradually increased. Initial results look promising, even in people with peanut allergy. But, more research needs to be done to ensure that this treatment is safe.



Adopted from mayoclinic.com