III.

Diagnosis and Treatment

Diagnosing and treating allergies is usually performed by an allergist, a physician trained to understand the body's immune response. When visiting an allergist for the first time, a patient is usually asked which substances seem to provoke symptoms and whether other family members have allergies. The doctor conducts a brief physical examination, looking in the nose, eyes, ears, and throat, listening to the chest, and examining the skin.

In many cases the allergist will perform allergy skin tests. These are painless injections or scratches into the surface of the skin with tiny amounts of specific allergens, such as pollens or house dust mites. The injection produces a tiny bump in the skin, no larger than the head of a pin. When a person has a positive skin test response (usually occurring after 15 to 30 minutes), there is a local reaction in the skin. The tiny bump gets slightly bigger, slightly itchy, and is surrounded by some redness caused by dilating blood vessels in the area. This reaction indicates to the allergist that cells in the skin contain specific antibodies to the allergens used in the injection. This reaction provides a quick technique for testing and diagnosing specific allergies. Sometimes blood samples evaluated in a laboratory are used to measure the blood levels of IgE antibodies specific to individual allergens, although skin tests have proven to be more accurate, faster, and less expensive in allergy diagnosis.

For most patients with allergies, medicines are used to begin therapy. Most forms of hay fever are easily managed with antihistamines, which relieve the symptoms, such as itching and sneezing, produced by histamine. Asthma is usually treated with medications taken orally or inhaled in vapor form using a metered-dose inhaler. Asthma medications include bronchodilators (drugs that expand the air passages) and anti-inflammatory steroids, which suppress the immune response that causes airway inflammation. In cases of anaphylactic shock, emergency treatment with an injection of adrenaline, also known as epinephrine, is required. This injection quickly widens blood vessels and opens up constricted airways.

If medicines cannot control allergy symptoms, the allergist may suggest allergen immunotherapy, a series of injections of the offending allergens. These injections, or allergy shots, help desensitize the patient to the allergens, thereby reducing the allergic response. For safety reasons, the injections begin with very small allergen doses, close to the amount used in a skin test. The amount of the allergen injected is increased each week for many weeks, until high doses of injected allergens are reached. The goal of immunotherapy is to produce blocking or neutralizing antibodies that provide a protective response in the cells, preventing allergens from binding to the allergic antibodies. When this blocking is achieved, little or no histamine is released in response to the allergens, and allergic symptoms are reduced or eliminated. Allergen immunotherapy is especially effective in overcoming stinging insect allergies, which, if left untreated, can result in a fatal allergic reaction to an insect bite. Immunotherapy is also effective for severe hay fever and, in some patients, for severe, chronic allergic asthma.

In many cases the best allergy treatment is the removal, if possible, of the offending allergens from the patient's environment. For example, the best way to deal effectively with an allergy to cats is to remove cats from the patient's surroundings, although desensitizing injections containing cat extracts are being tested. Unfortunately, some allergens, such as plant pollens, are impossible to avoid, since they float freely through the air. Contact with pollens can be reduced by keeping windows closed and using air conditioners to filter and cool indoor air. House dust mites, a common allergen, can be minimized by frequent cleaning with safe chemicals.

Food allergies are more difficult to diagnose and treat than other types of allergies. Skin tests are unreliable, and blood tests can be inconclusive. When a particular food is suspect, the patient simply should not eat it. If the culprit food is unknown, the allergist may put the patient on a special diet that eliminates various foods. If symptoms decline, the allergist will reintroduce each of the foods one at a time to help identify which food is the offending allergen. To help patients identify possible food allergens in packaged or processed food, the U.S. Congress in 2004 enacted the Food Allergen Labeling and Consumer Protection Act. The law, which went into effect in January 2006, requires food manufacturers to clearly label ingredients in their products that are derived from the eight major food allergens. Under the law, food labels must contain a box near the ingredients list that specifies the food allergens in the product. Within the ingredients list, the common name for a food allergen must be provided next to the scientific or technical name. See also Food Processing and Preservation.