Confused about how to deal with common food allergies? Not sure where to even start? Clifford W. Bassett, M.D., a medical director of Allergy & Asthma Care of New York and a faculty member at the New York University School of Medicine, provides practical advice for managing food allergies in the primary-care setting:

Q: At what ages do most patients develop food allergies? Can they suddenly show up in adults?
A: Most food allergies develop in children 6 years of age or younger, but they can occur for the first time at any age, including in adulthood. The estimated prevalence of food allergy among American children is 5-7 percent. In adults, it is about 1-2 percent. Interestingly, roughly 25 percent of adults recently polled believe they have food allergies or know someone who does.

Q: What causes a food allergy?
A: The reactions seen in food allergy are due to allergen-antibody interaction. Both genetics and environment influence the risk. The “atopic” or allergic predisposition to a food allergy has been noted to be higher in an individual with a strong family history of allergy. Environmental factors then contribute to the expression of that allergy.

Food allergies are increasing in children. In 2002, studies reported that the prevalence of peanut allergy had doubled over the past decade.

Q: What are the typical symptoms?
A: The most common skin symptom is a “hive.” According to recent review, almost 90% of symptoms affect the skin, with the next most common symptoms affecting the respiratory system and structures. The spectrum of true food-allergy reactions includes nasal congestion; itchiness of the ears, mouth, and throat; swelling of the face/tongue; cough; trouble breathing; itchiness of the skin; and hives.

Reaction severity can vary with the amount of food ingested and the combination with other foods or alcohol. Even exercise may provoke or worsen reactions, especially in food-dependent, exercise-induced allergic urticaria/anaphylaxis.

Most allergic individuals experience true symptoms with ingestion, but inhalation of the allergen or skin contact may also precipitate a reaction. The reactions of a few passengers who inhaled air that had been in contact with peanuts has led some airlines to stop serving peanuts.

Q: What foods cause the most allergies in children?
A: Eight foods — cow’s milk, egg, peanut, tree nuts, fish, shellfish, soybean and wheat — account for 90 percent of all food allergies. Allergy to cow’s milk will increase an infant’s future risk of developing other food allergies, and milk is often hidden in other foods.

Q: Are there any preventive measures?
A: Recommendations have included breast-feeding for a period of 6-12 months, a delay in the introduction of solid foods, and avoiding peanut and tree nuts, which may reduce the risk of allergy.

Q: What about wheat products?
A: Wheat products are among the eight foods reported to be responsible for about 90% of allergic reactions to food in children. Immunoglobulin E (IgE)-mediated allergic reactions may occur to wheat. Of course, other adverse reactions to ingested wheat do occur, in particular, celiac disease in children and adults. Celiac disease, also known as “gluten intolerance,” is a genetic disorder that can present in a variety of ways, including diarrhea, weight loss and malnutrition.

The only treatment for celiac disease is strict adherence to a 100% gluten-free diet.

Q: What are the most common food allergies in adults?
A: In adults, the most common allergies are to peanuts, other nuts (known as “tree nuts”), fish and shellfish. Allergy to peanuts affects 0.6 percent of the U.S. population and is usually severe in its presentation. Tree-nut allergy affects about 0.5 percent of the population. Tree-nut reactions can also be quite severe and account for a high percentage of fatal food reactions.

With some food families, especially tree nuts and seafood, an allergic sensitivity to one food in a group may confer an allergic sensitivity to other foods in the food group. For example, if a person is allergic to walnuts (which are in the tree-nut family), that individual may be more likely to be allergic to almonds or pecans or other nuts within that family. Those allergic to peanuts should avoid peanut oil and peanut butter and use caution with cuisines containing peanut products, such as Asian, Thai, Mexican and Vietnamese foods. Moreover, various nut proteins can hide and/or masquerade in items you may not expect to contain these ingredients, such as baked goods, various flavorings and even packaged sunflower seeds.

Allergic reactions to shellfish (shrimp, crab, lobster, clam, oyster, etc.) can induce a variety of mild to severe reactions. Reactions to many different types of shellfish in an individual is commonly seen.

Q: Peanuts are ubiquitous in the American diet. Is there a checklist you give patients for avoiding peanuts in all their forms?
A: The Food Allergy and Anaphylaxis Network (FAAN) is a good resource for patients with food allergies, including those with peanut allergies (www.foodallergy.org).

Q: Do patients ever outgrow food allergies?
A: Some certainly do. But the only sure way to prevent bad outcomes is strict avoidance of an allergy-causing food. Food allergies to shellfish and peanuts/nuts are lifelong in about 80% of individuals affected. About 6-8 percent of children younger than 3 years experience food-allergic reactions. Many of these children will “outgrow” such reactivity by age 10 years. Hugh A. Sampson, M.D., of Mount Sinai Medical Center in New York City, a leading investigator of food allergy, reported that about 85 percent of cow’s milk and 80 percent of egg-allergic children will outgrow these allergies.

Q: How do you test for food allergy?
A: Skin and blood tests to food allergens are often diagnostic. If, over time, a positive test becomes negative, it is possible that a person will tolerate the food. Some people, however, will continue to have positive test reactivity to foods they tolerate without apparent harm.

Recent studies done by Dr. Sampson’s group have shown that if the serum level of IgE antibodies to a food falls below a certain point, there is at least a 60 percent chance that allergy to that food has been lost. To be certain about this, an allergist will sometimes perform an oral food challenge in the office. The patient is given a sample of the food, and his or her reaction is carefully monitored.

Some hidden sources of milk

• Deli meat slicers used for both meat and cheese products.

• Some brands of canned tuna fish contain casein (a milk protein).

• Many nondairy products list casein on their ingredient labels.

• Some meats may contain casein as a binder. Check all labels carefully.

• Many restaurants put butter on steaks after they have been grilled to add extra flavor. The butter is not visible after it melts.

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