Encyclopedia of Health and Medicine

allergy 243
Such medications typically include antihistamine
nasal sprays, corticosteroid nasal sprays, oral ANTI-
HISTAMINE MEDICATIONS, and oral decongestant medications.
Another classification of DRUG that is
sometimes effective for allergic rhinitis is the
leukotriene receptor antagonist, which blocks the
action of LEUKOTRIENES (other chemicals that mediate
the IMMUNE RESPONSE). The leukotriene receptor
antagonist medication approved for use in the
United States is montelukast (Singulair). Cromolyn
sodium nasal spray targets mast cells,
reducing their ability to release immune mediator
chemicals such as histamine, PROSTAGLANDINS, and
leukotrienes. DESENSITIZATION, commonly called
allergy shots, is an option for some people. Desensitization
works by exposing the IMMUNE SYSTEM
to small amounts of the allergen over time to
retrain the immune response to ignore the allergen.
Older antihistamine medications such as
diphenhydramine (Benadryl) are very effective
though cause drowsiness. Newer antihistamine
medications such as loratadine (Claritin) are
equally effective for most people and cause significantly
less drowsiness. Antihistamines block the
action of histamines, chemicals that mediate (initiate
and facilitate) the processes of the immune
response that result in the symptoms. Most antihistamines
are available as OVER-THE-COUNTER (OTC)
DRUGS that do not require a doctor’s prescription.
GINGER, available in various preparations, contains
a mild antihistamine.
Oral decongestant medications available over
the counter in the United States are pseudoephedrine
and phenylephrine, though there are
several OTC decongestant nasal sprays. Many OTC
allergy products combine a decongestant with an
antihistamine. Decongestants work by constricting
the BLOOD vessels in the nasal mucosa, reducing
the availability of fluid to the tissues. Chronic or
long-term use of decongestants can result in
rebound congestion, a condition in which the
nasal membranes swell in the absence of the
decongestant. Nose drops and nasal sprays containing
saline (salt solution) are often as effective
in relieving congestion. They work by soothing
the nasal mucosa and flushing away topical irritants,
including allergens.
Risk Factors and Preventive Measures
Allergic rhinitis is very common, affecting 20 percent
of the American adult population. The most
effective measure to reduce symptoms is to limit
or eliminate exposure to the allergens that trigger
the hypersensitivity response. Many people are
able to mitigate symptoms by using allergy medications
regularly for the duration of the allergy
season.
There appears to be a GENETIC PREDISPOSITION for
chronic allergic rhinitis, also called atopic rhinitis,
which has more extensive symptoms that tend to
be more perennial (ongoing) than seasonal. People
who have atopic rhinitis have increased risk
for other atopic conditions such as ALLERGIC
ASTHMA (also called atopic asthma), atopic CON-
JUNCTIVITIS, and atopic DERMATITIS. A flare of symptoms
in one atopic condition often brings on
symptoms in another.
See also ALLERGIC DERMATITIS; ANTIBODY; CORTICO-
STEROID MEDICATIONS; IMMUNOTHERAPY; LIVING WITH
ALLERGIES; MAST CELL; SINUSITIS.
allergy An abnormal sensitivity to an ordinarily
harmless substance, called an ALLERGEN, that produces
a HYPERSENSITIVITY REACTION (allergic reaction)
in response to the IMMUNE SYSTEM’s detection of the
substance’s presence. A person can have an allergy
to nearly any substance. Though researchers
understand the mechanisms of hypersensitivity
reaction, they do not know what causes the
immune system to determine the substance is a
potential invader. The first exposure to the substance
activates an immune response that stimulates
B-lymphocytes (specialized white BLOOD
cells) to produce antibodies. Second and subsequent
exposures engage the ANTIBODY response, in
which the antibodies bind with molecules bearing
the allergen to mark them for destruction.
Allergies are common. Symptoms vary according
to the allergen. Some symptoms remain localized,
affecting only a distinct part of the body
(such as in ALLERGIC DERMATITIS or ALLERGIC
RHINITIS). Others are systemic, affecting the body as
a whole (such as hypersensitivity reaction to a
drug or a food item). A severe hypersensitivity
reaction can cause life-threatening swelling of the
THROAT and airways (ANAPHYLAXIS).