"Hey, do you want some?" your friend asks as he offers you a mouthwatering homemade brownie. You're tempted by the delicious dessert, but then you see the crushed peanuts on top. Darn! You're allergic to peanuts. Maybe just one little bite?

Nope. If you have a food allergy, even a very tiny bit of that food can make you sick. It's better to say "no, thanks" to the brownie and have a nut-free dessert.

Lots of kids have food allergies — about 3 million in the United States alone. These foods cause the most food allergies:

• peanuts and other nuts
• seafood, such as shrimp
• milk, particularly cow's milk
• eggs
• soy
• wheat

What Is a Food Allergy?

Food allergies occur when your immune system makes a mistake. Normally, your immune (say: ih-myoon) system protects you from germs and disease. It does this by making antibodies that help you fight off bacteria, viruses, and other tiny organisms that can make you sick. But if you have a food allergy, your immune system mistakenly treats something in a certain food as if it's really dangerous to you.

The same sort of thing happens with any allergy, whether it's a medicine (like penicillin), pollen in the air (from flowers and trees), or a food, like peanuts. So the thing itself isn't harmful, but the way your body reacts to it is.

What's a Reaction Like?

If a kid with peanut allergy would have eaten that peanut-topped brownie, here's what would happen. Antibodies to something in the food would cause mast cells (a type of immune system cell in the body) to release chemicals into the bloodstream. One of these chemicals is histamine (say: his-tuh-meen).

The histamine then causes symptoms that affect a person's eyes, nose, throat, respiratory system, skin, and digestive system. A person with a food allergy could have a mild reaction — or it could be more severe. An allergic reaction could happen right away or a few hours after the person eats it.

Some of the first signs that a person may be having an allergic reaction could be a runny nose, an itchy skin rash such as hives, or a tingling in the tongue or lips. Other signs include:

• tightness in the throat
• hoarse voice
• wheezing
• cough
• nausea
• vomiting
• stomach pain
• diarrhea

In the most serious cases, a food allergy can cause anaphylaxis (say: ah-nuh-fuh-lak-sis). This is a sudden, severe allergic reaction in which several problems occur all at once and can involve the skin, breathing, digestion, the heart, and blood vessels. A person's blood pressure can drop, breathing tubes can narrow, and the tongue can swell.

People at risk for this kind of a reaction have to be very careful and need a plan for handling emergencies, when they might need to get special medicine to stop these symptoms from getting worse.

Many kids outgrow allergies to milk and eggs as they grow older. But severe allergies to foods like peanuts, certain kinds of fish, and shrimp often last a lifetime.

How Do You Know if You Have One?

Sometimes it's easy to figure out that a kid has a food allergy. He or she might get hives or have other problems after eating it. But other times, what's causing the problem is more of a mystery. Most foods have more than one ingredient, so if a kid has shrimp with peanut sauce, what's causing the allergy — the peanut sauce or the shrimp?

Doctors believe that allergies could be hereditary, which means if your parent or another close relative has certain allergies like hay fever, you're more likely to develop the allergies. Some kids are born allergic to certain foods, whereas others develop food allergies over time. This may be due to someone's surroundings or changes in the body as they grow older.

Many people react to a certain food but are not actually allergic. For example, people with lactose intolerance (say: lak-tose in-tah-luh-runtz) get belly pain and diarrhea from milk and other dairy products. That doesn't mean they're allergic to milk. They don't feel good after drinking milk because their bodies can't properly break down the sugars found in milk.

What Will the Doctor Do?

If you think you may be allergic to a certain food, let your parents know. They will take you to the doctor to get it checked out.

If your doctor thinks you might have a food allergy, he or she will probably send you to see a doctor who specializes in allergies. The allergy specialist will ask you about past reactions and how long it takes between eating the food and getting the symptom (such as hives). The allergist also may ask about whether anyone else in your family has allergies or other allergy-related conditions, such as eczema or asthma.

The allergist might want to do a skin test. This is a way of seeing how your body reacts to a very small amount of the food that is giving you trouble. The allergist will use a liquid extract of the food and, possibly, other common allergy-causing foods to see if you react to any of them. (A liquid extract is a liquid version of something that usually isn't liquid.)

The doctor will make a little scratch on your skin (it will be a quick pinch) and drop a little of the liquid extract on the scratched spot or spots. Different extracts will go on the different scratch spots, so the doctor can see how your skin reacts to each substance. If you get a reddish, raised spot, it shows that you are allergic to that food or substance.

Some doctors may also take a blood sample and send it to a lab. That's where it will be mixed with some of the food or substance you may be allergic to and checked for certain antibodies.

It's important to remember that even though the doctor tests for food allergies by exposing you to a very small amount of the food, you should not try this at home! The best place for an allergy test is at the doctor's office, where the staff is specially trained and could give you medicine right away if you had a serious reaction.

How Are Food Allergies Treated?

There is no special medicine for food allergies. Some can be outgrown; others will last a kid's whole life. The best treatment is simply to avoid the food itself and any foods or drinks that contain the food.

One way to figure that out is to read food labels. Any foods that might cause an allergic reaction will be listed near or in the ingredient list. Doctors and allergy organizations also can help by providing lists of safe foods and unsafe foods. Some people who are very sensitive may need to avoid foods just because they are made in the same factory that also makes their problem food. You may have seen some candy wrappers that say the candy was made in a factory that processes nuts, too.

Have a Plan

No matter how hard you try, you may eat the wrong thing by accident. Stay calm and follow your emergency plan. What's an emergency plan? Before a slip-up happens, it's a good idea to create a plan with your doctor and parents. The plan should spell out what to do, who to tell, and which medicines to take if you have a reaction.

This is especially important if you have a food allergy that can cause a serious reaction (anaphylaxis). For serious reactions, people may need a shot of epinephrine (say: eh-pih-neh-frin) with them. This kind of epinephrine injection comes in an easy-to-carry container that looks like a pen. You and your parent can work out whether you carry this or someone at school keeps it on hand for you. You'll also need to identify a person who will give you the shot.

You might want to have antihistamine medication on hand as well, though if anaphylaxis is occurring, this medicine is not a substitute for epinephrine. After receiving an epinephrine shot, you would need to go to the hospital or a medical facility, where they would keep an eye on you and make sure the reaction is under control.

Living With Food Allergies

Having a food allergy is a drag, but it doesn't need to slow a kid down. Your mom, dad, and other adults also can help you steer clear of reactions.

But what if something you really like turns out to be on your "do not eat" list? Today, so many people have food allergies that companies have created lots of good substitutes for favorite foods — everything from dairy-free mashed potatoes to wheat-free chocolate chunk cookies!

Reviewed by: Steven Dowshen, MD
Date reviewed: January 2012