Allergies Health Article

When to call the doctor

Parents should consult a physician when a child has repeated and prolonged symptoms. Allergic rhinitis may be mistaken for a cold or other upper respiratory infection. Usually, a fever indicates an infection. Food allergies and allergies to insect stings or medications can be especially dangerous, causing anaphylactic reactions that require emergency treatment.

Diagnosis

Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy is suspected if the symptoms presented are characteristic of an allergic reaction, and this occurs repeatedly upon exposure to the suspected allergen. Allergy tests can also be conducted to determine allergens.

Skin tests

Skin tests are performed by administering a tiny dose of the suspected allergen by pricking, scratching, puncturing, or injecting the skin. The allergen is applied to the skin as an aqueous extract, usually on the back, forearms, or top of the thighs. Once in the skin, the allergen may produce a classic immune wheal and flare response (a skin lesion with a raised, white, compressible area surrounded by a red flare). The tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. A positive reaction occurs on the skin even if the allergen is at levels normally encountered in food or in the airways. Reactions are usually evaluated approximately 15 minutes after exposure. Intradermal skin tests involve injection of the allergen into the dermis of the skin. These tests are more sensitive and are used for allergies associated with risk of death, such as allergies to antibiotics. Skin testing may be painful for children.

Provocation tests

These tests involve the administration of allergen to elicit an immune response. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Delayed

allergic contact dermatitis diagnosis involves similar methods by application of a skin patch with allergen to induce an allergic skin reaction. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount of the test substance administered as an opaque capsule along with a placebo control. Provocation tests are not used if anaphylaxis is a concern given the patient's medical history.

Treatment

Avoiding allergens is the first line of defense to reduce the possibility of an allergic attack. However, complete environmental control is often difficult to accomplish; hence, therapeutic interventions are usually necessary. A large number of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most of these products 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.

Antihistamines

Antihistamines are drugs used to treat the symptoms of allergic rhinitis by blocking the action of histamine, a chemical released by the immune system in allergic reactions. Antihistamines are available as prescription and over-the-counter tablets, topical gels or creams, nasal sprays, and eye drops.

Commonly used antihistamines include the following:

• diphenhydramine (Benadryl)
• loratadine (Claritin)
• cetirizine (Zyrtec)
• fexofenadine (Allegra)
• clemastine fumarate (Tavist)
• chlorpheniramine (Chlor Trimeton)
• brompheniramine (Dimetapp)

Decongestants

Decongestants dry up nasal passage tissues and reduce swollen nasal membranes so as to relieve congestion. Decongestants are available as nasal sprays or drops, oral tablets, or syrups. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, and agitation. Use of nasal spray decongestants for longer than four to five days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment. Saline nasal sprays, which do not contain decongestants, may be used for longer periods of time to help congestion and nasal passage irritation.

Commonly used decongestants include the following:

• oxymetazoline (Afrin)
• pseudoephedrine (Sudafed)
• phenylephrine (Neo Synephrine)