Food allergies have generated a great deal of anxiety in recentyears, with some schools going so far as to ban popular staples —especially peanut butter — after appeals from worried parents.

Some airlines have quit serving peanut snacks, and more and morerestaurants are offering dishes for diners concerned about glutenor dairy allergies.

There is no question that some foods, especially peanuts andshellfish, can provoke severe reactions in a small fraction of thepopulation. but a new analysis finds that many children and adultswho think they have food allergies are mistaken.

According to a definitive report compiled for the NationalInstitute of Allergy and Infectious Diseases by a 25-member panelof experts, a big part of the problem is misdiagnosis, fromoverreliance on two tests — a skin-prick test and a blood test forantibodies — that can produce misleading results.

The mere presence of antibodies to a particular substance infood does not mean that someone is allergic to that food. Nor doesa reaction to a skin prick with a suspect food; in fact, askin-prick test can remain positive long after an allergy isgone.

Sometimes a diagnosis is based on no test at all, solely on apatient’s or parent’s report of a bad reaction after a particularfood was eaten. People often mistake food intolerance, likedifficulty digesting the lactose in milk, for an allergy.(Allergies involve the immune system; lactose intolerance resultsfrom deficiency of an enzyme.)

The only test that can definitively establish a food allergy isa so-called oral challenge, in which the patient ingests thesuspect food and waits for a reaction. This can be safely done onlyby an experienced health professional with emergency treatment athand in case of a severe reaction.

Understandably, doctors are often reluctant to try an oralchallenge. but in challenges where a suspect food is compared witha placebo and neither doctor nor patient knows which food is which,only about a third of the foods have been found to cause allergies,the panel reported.

Nonetheless, genuine food allergies seem to have risen duringthe last decade or two, for reasons no one knows, said Dr. AnthonyS. Fauci, director of the allergy institute. the institute, adivision of the National Institutes of Health, sponsored thepanel’s two-year effort to establish national guidelines for thedefinition, diagnosis and treatment of food allergies.

According to the panel’s detailed and well-documented report,about one child in 20 and one adult in 25 has a food allergy,nowhere near popular estimates that up to 30 percent of Americansare afflicted.

The panel also reported that most children outgrow allergies tomilk, egg, soy and wheat, but until they are properly tested theymay not know it is now safe to eat the food — or, perhaps moreimportant, to receive a vaccine prepared in eggs.

Allergies to peanuts and tree nuts are relatively rare (abouthalf of 1 percent of the population in each case, according to thepanel). but they tend to be lifelong and life-threatening, and canrequire extreme vigilance.

Some food allergies start in adulthood, and tend to lastindefinitely as well. in particular, shellfish allergies, which canbe life-threatening, occur in only 0.5 percent of children but 2.5percent of adults.

It is not possible to predict the severity of a food allergyreaction based on past reactions. in the case of nut allergy, forexample, subsequent exposures can be much worse than what a childfirst experienced.

There are no treatments for food allergy except to avoid theculprit food, which may require careful reading of labels andpotentially embarrassing inquiries when eating away from home.Although immunotherapy has been proposed as a means of curbing anestablished food allergy, the panel did not recommend this outsideof “highly controlled clinical settings.”

Many packaged food labels now warn not only that a particularallergen is present, but also that the product was prepared whereallergens like nuts, wheat or soy are present. but Mount SinaiMedical Center in Manhattan did a study of parents’ label readingand found that they were surprisingly poor at identifying foods towhich their children were allergic.

Symptoms of food allergies are often confusing and can bemistaken for other problems. they can affect the skin (for example,as eczema or hives), eyes, upper or lower respiratory tract, anypart of the digestive tract, and the cardiovascular system. Butunless a food allergy is proved, the panel does not recommendavoiding foods to control allergic dermatitis, asthma orinflammation of the esophagus.

As for vaccines, the panel said that even children with an eggallergy could safely be immunized for measles, mumps, rubella andvaricella (chickenpox), but the flu vaccine should not begiven.

WHEN, WHEN NOT TO WORRY

The experts found little evidence that restricting a woman’sdiet during pregnancy and lactation was effective in preventingfood allergies in her offspring. Nor did they find strong evidencethat exclusive breast-feeding for four to six months can preventallergic disease. the panel said substituting soy for cow’s milkinfant formula did not prevent food allergies in infants thought tobe at risk because of a family history of allergy.

Moreover, there is danger in restricting children’s diets forfear of allergies, even real ones: they can develop nutrientdeficiencies that result in retarded growth and development. Thus,the panel recommended “nutritional counseling and regular growthmonitoring for all children with food allergies.”

The panel devoted the last section of its lengthy report tofood-induced anaphylaxis, a potentially fatal disorder that isoften recognized too late for adequate treatment. the most commonfood causes of anaphylaxis, the panel said, are peanuts, tree nuts,milk, eggs, fish and crustacean shellfish, and a life-threateningreaction can occur even the first time a person is exposed.

Symptoms that occur within minutes to several hours afterexposure may involve lesions of the skin and mouth; difficultybreathing; a precipitous drop in blood pressure, dizziness or rapidheart rate; abdominal pain, vomiting or diarrhea; and anxiety,mental confusion, lethargy or seizures.

Anyone with a life-threatening food allergy must always havereadily available two doses of self-injectable epinephrine(commonly known by the brand EpiPen), to be injected into the thighmuscle. Treatment with an antihistamine is not an effectivesubstitute, the panel warned.

Fatalities result when the use of epinephrine is delayed or thedose given is inadequate. When in doubt, treat, the panel said;then call 911. the EpiPen is a stopgap measure to buy time untillife-saving care can be administered.

Parents, baby sitters, school nurses and camp counselors musthave two epinephrine pens handy and know how to use them for eachchild at risk of anaphylaxis. the pens must be stored at 59 to 89degrees Fahrenheit, and must be replaced annually.