Allergies Health Article

Symptoms

Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose, often with a scratchy or irritated throat due to post-nasal drip. Allergic conjunctivitis (inflammation of

the thin membrane covering the eye) causes redness, irritation, and increased tearing in the eyes. Asthma causes wheezing, coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether it is spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat, and nausea, cramping, diarrhea, and gas. Contact dermatitis is marked by reddened, itchy, weepy skin blisters.

Systemic reactions may occur from any type of allergen, but are more common following ingestion or injection of an allergen. Skin reactions include hives and angioedema (a deeper and more extensive skin reaction) involving more extensive fluid collection. Anaphylaxis is marked by airway constriction, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, and, in some cases, loss of consciousness.

Diagnosis

Allergies may often be diagnosed by taking a detailed medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy tests may be used to identify potential allergens. These tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. Reaction will occur on the skin even if the allergen is normally encountered in food or in the airways.

RAST testing, performed by a laboratory technologist, is a blood test that measures the level of reactive IgE antibodies in the blood. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount.

Treatment

A variety of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing immune responses in general.

Drugs

ANTIHISTAMINES. Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine released by mast cells. They may be used after symptoms appear, though they may be even more effective when used before symptoms appear. A wide variety of antihistamines are available.

Some antihistamines produce drowsiness as a major side effect. These include:

• diphenhydramine (Benadryl and generics)
• chlorpheniramine (Chlor-trimeton and generics)
• brompheniramine (Dimetane and generics)
• clemastine (Tavist and generics)

Antihistamines that do not cause drowsiness are available by prescription and include the following:

• astemizole (Hismanal)
• loratidine (Claritin)
• fexofenadine (Allegra)
• azelastin HCl (Astelin)

Hismanal has the potential to cause serious heart arrhythmia when taken with the antibiotic erythromycin, the antifungal drugs ketoconazole and itraconazole, or the antimalarial drug quinine. Exceeding the recommended dose of Hismanal may also cause arrhythmia.

DECONGESTANTS. Decongestants constrict blood vessels to counteract the effects of histamine. Nasal sprays, applied directly to the nasal lining and oral systemic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, and agitation. Use of topical decongestants for longer than several days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment.

TOPICAL CORTICOSTEROIDS. Topical corticosteroids reduce mucous membrane inflammation and are available by prescription. Allergies tend to worsen as the season progresses because the immune system becomes sensitized to particular antigens and can produce a faster, stronger response. Topical corticosteroids are especially effective at reducing this seasonal sensitization because they work more slowly and last longer than most other medication types. As a result, they are best started before allergy season begins. Side effects are usually mild, but may include headaches, nosebleeds, and unpleasant taste sensations.

MAST CELL STABILIZERS. Cromolyn sodium prevents the release of mast cell granules, thereby preventing the release of histamine and other chemicals contained in them. It acts as a preventive treatment if it is begun several weeks before the onset of the allergy season. It also may be used for year round allergy prevention. Cromolyn sodium is available as a nasal spray for allergic rhinitis and in aerosol (a suspension of particles in gas) form for asthma.