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as oak, ash, and elm), and weeds (such as ragweed). Most people experience symptoms in the spring or fall, but exactly when a plant pollinates depends on its geographic location. Weather conditions don’t affect the amount of pollen but influence the amount that gets distributed. For example, pollen counts are highest on warm, dry days and lowest on cold, wet days. If you have hay fever, stay indoors as much as possible with the windows closed when you are having symptoms or when pollen counts are high. Use air-conditioning and heating systems with built-in filters (smaller air-filtering machines may not be effective). Resist rubbing your eyes, which can make the irritation worse.

If over-the-counter medications don’t relieve your symptoms, your doctor may prescribe an antihistamine that doesn’t cause drowsiness. Eyedrops prescribed by your doctor can temporarily relieve eye irritation. Corticosteroid nasal sprays work well to relieve nasal congestion and the trickle of nasal secretions down the back of the throat (called post-nasal drip). In rare cases, a doctor may also prescribe medications usually used to treat asthma—such as bronchodilators (see page 641) to open the airways, or corticosteroids taken by mouth or through an inhaler to reduce inflammation. If these medications don’t control the symptoms or if they cause adverse reactions, desensitization (see page 913) therapy may be recommended.

Allergies to Food

A food allergy is an allergic reaction to particular foods or food additives. The reaction usually occurs immediately or within a few hours after eating. In celiac disease (see page 768), in which the small intestine is hypersensitive to the protein gluten, the reaction may not occur until days later. Food allergies can last a lifetime, but many food allergies diagnosed in childhood disappear as the child gets older. The most common foods that cause allergies are nuts (especially peanuts, walnuts, and Brazil nuts), legumes (such as soybeans), fish and shellfish (especially whitefish and shrimp), cow’s milk, egg whites, and wheat. Food allergies tend to run in families.

Some people have abnormal reactions (such as indigestion; see page 749) to certain foods or beverages, but these reactions are not allergic because they don’t involve the immune system. Lactose intolerance (see page 770) is an adverse reaction (but not an allergic reaction) to dairy products. Some substances, including sulfites in wine or monosodium glutamate (MSG) in food, can cause chemical disturbances in the body but are not true allergens.

Symptoms

Once the allergy-causing food is absorbed into the bloodstream, it can react with antibodies (infection-fighting proteins) in the blood vessels, causing headaches, rashes, itching and swelling in the throat and around the lips and mouth, a stuffy or runny nose, or shortness of breath or difficulty breathing. Other symptoms of food allergies include abdominal swelling and pain, gas, nausea, vomiting, and diarrhea. In some cases, a person may have a life-threatening allergic reaction called anaphylactic shock (see below and next page).

WARNING!

Anaphylactic Shock

If you experience any of the following symptoms (especially after eating an unfamiliar food, being bitten or stung by an insect, or having an injection of a medication), call 911 or your local emergency number, or go to the nearest hospital emergency department immediately:

• Severe itching or a rash over several areas of your body

• Swollen lips, tongue, or throat

• Excessive sweating or cold, clammy skin

• Difficulty swallowing

• Difficulty breathing

• Difficulty speaking

• Vomiting

• Confusion

Diagnosis

To diagnose a food allergy, your doctor may recommend that you keep a food diary so he or she can see what kinds of foods you have eaten when you experience symptoms. The doctor may also put you on an exclusion diet (also called an elimination diet) in which, one by one, you eliminate the foods from your diet that are suspected of causing your allergy, to see if you no longer