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Hay Fever
| Definition |
| A collection of symptoms that occur
after exposure to airborne pollens of certain seasonal plants (see also
asthma; allergy to mold, dander, dust). |
| Alternative names |
| hay fever |
| Causes, incidence, and risk factors |
Allergies are caused by
hypersensitivity of the immune system, leading to a misdirected immune
response. The immune system normally protects the body against harmful
substances such as bacteria, viruses, and toxins. Allergy occurs when
the immune system reacts to substances (allergens) that are generally
harmless and in most people do not cause an immune response.
Hay fever (allergic rhinitis) involves an allergic reaction to pollen. A
virtually identical reaction occurs with allergy to mold, animal dander,
dust, and similar inhaled allergens. The pollens that cause hay fever
vary from person to person and from region to region. Pollens that are
carried by bees from plant to plant are seldom responsible for hay fever
because the grains are large and have a waxy coating. Pollens that are
carried by the wind are smaller and more often cause hay fever. Examples
of plants commonly responsible for hay fever include:
- trees (deciduous and evergreen)
- grasses
- most flowers
- ragweed
In addition to individual sensitivity
and regional plant prevalence, the amount of pollen in the air can be a
factor in whether hay fever symptoms develop. Hot, dry, windy days are
more likely to have increased amounts of pollen in the air than cool,
damp, rainy days where pollen is washed to the ground.
When an allergen such as pollen enters the body of a person with a
sensitized immune system, it triggers antibody production. Histamine and
other chemicals are released by body tissues as part of the immune
response. This causes itching, swelling of affected tissues, mucus
production, muscle spasms, and other symptoms.
Many disorders are associated with, triggered, or worsened by allergies.
These include eczema, asthma, and many others.
Allergies are very common. Heredity, environmental conditions, number
and type of exposures, emotional factors (stress and emotional upset can
increase the sensitivity of the immune system), and many other factors
can indicate a predisposition to allergies.
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| Prevention |
There is no known way to prevent
development of hay fever.
Symptoms may sometimes be prevented by avoiding known allergens. Most
trees produce pollen in the spring, grasses and flowers usually produce
pollen during the summer, and ragweed and other late-blooming plants
produce pollen during late summer and early autumn. During the
pollen-producing times ("pollen season"), people with hay
fever should remain indoors in an air conditioned-atmosphere whenever
possible. |
| Symptoms |
- coughing
- headache
- itching of the nose, mouth, eyes,
throat, skin, or any area
- runny nose (rhinitis)
- smell, impaired
- sneezing, may be frequent
- stuffy nose (nasal congestion)
- tearing, increased
- throat, sore
- wheezing
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| Signs and tests |
History is important in diagnosing
allergies, including whether the symptoms vary according to time of day
or the season and possible exposures.
- Immunoelectrophoresis - serum will
show antibody (particularly IgE) levels that are elevated indicate
allergic reaction.
- Complement levels may be abnormal.
- Allergy testing may reveal the
specific allergen(s). Skin testing is the most common method of
allergy testing. This may include intradermal, scratch, patch, or
other tests. Occasionally, the suspected allergen is dissolved and
dropped onto the lower eyelid (conjunctiva) of the eye as a means of
testing for allergies.
- Other testing to determine the
specific allergen may include various types of "use" or
"elimination" tests where suspected items are eliminated
and/or introduced while the person is observed for response to the
substance.
This disease may also alter the
results of an eosinophil count - absolute test.
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