Allergic reactions to food are rarely fatal, but they can be: Anaphylaxis (an extreme allergic reaction) can close up a child's throat so he can't breathe. If you suspect this might be happening, call 911 immediately.

Fortunately, most of the time allergies cause less severe symptoms, such as a rash around the mouth, hives, eczema, sneezing, a runny nose, or wheezing. Watch for a pattern  -- a reaction that appears a few minutes to two hours after eating and occurs each time your child has even the slightest bit of the problem food.

Ease symptoms right away with an anti-allergy medication that contains diphenhydramine (like Benadryl), which blocks histamines, the chemicals that cause allergic symptoms. The liquid form gets into the system faster than chewables, says Hugh Sampson, M.D., director of the Jaffe Food Allergy Institute and professor of pediatrics at Mount Sinai School of Medicine, in New York City. Stop giving your child the suspect food until he sees a doctor.

"The sooner your child is evaluated and stops eating the food, the more likely he'll outgrow the allergy," says Dr. Sampson. (About 80 percent of kids with egg and milk allergies outgrow them by age 4; 20 percent of those with peanut allergies, by age 5.) On PopSci.com: Why are so many kids allergic to peanuts?

The doctor will likely refer you to an allergist, who'll do a skin-prick test followed by a blood test. If these suggest only a slight problem, your child may then be given a test called a food challenge: In an allergist's office, he'll eat gradually increasing amounts of the suspect food to see whether it really does cause a reaction. If a food allergy is diagnosed:

Be a label sleuth.

For example, foods that contain "casein" or "whey" are off-limits if your child is allergic to milk products.

Prepare for emergencies.

If there's a potential for anaphylaxis, the doctor will prescribe epinephrine, given by self-injection (the EpiPen) to treat severe reactions. Learn how to use it yourself and make sure those who care for your child do too.

Broadcast the news.

Tell everyone at daycare, home, and school which foods your child must avoid. Gently explain to him that he's to eat only food that you give him.

To learn more, log on to the Food Allergy & Anaphylaxis Network: www.foodallergy.org.

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