Alternate Names: Hay fever
Causes and Risks: 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.
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:
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.
Treatment: The goal of treatment is reduction of allergy symptoms.
Avoidance is the best treatment (see Prevention). Complete avoidance of environmental allergens may be impossible, but exposure may be minimized in many cases.
Antihistamines such as diphenhydramine often provide good relief of mild to moderate symptoms. For people with severe or frequent hay fever symptoms, the health care provider may prescribe an antihistamine that is long-acting and less likely to cause drowsiness than over-the-counter antihistamines. Decongestants may also be helpful in reducing symptoms such as nasal congestion. Corticosteroids reduce the immune response and may be prescribed to reduce severe symptoms.
Other medications may vary depending on the type and severity of symptoms.
Specific illnesses that are caused by allergies (such as asthma and eczema) may require other treatments.
Desensitization (immunotherapy, "allergy shots") is occasionally recommended. It includes regular injections of the allergen, given in increasing doses (each dose is slightly larger than the previous dose) that may "acclimatize" the body to the antigen.
Prognosis: Most allergies are readily treated. However, treatment only affects that exposure, so subsequent exposures will cause another allergic reaction.
Rarely, people may outgrow an allergy as the immune system becomes less sensitive to the allergen. However, as a general rule, once a substance has provoked an allergic reaction it continues to affect the person.
Desensitization may cause uncomfortable side effects (such as hives and rash) and may have dangerous side effects such as anaphylaxis. It often requires years of treatment and is effective in about two-thirds of cases.
Complications:
- discomfort during the allergic reaction
- disruption of lifestyle (rare)
- drowsiness and other side effects of antihistamines
- side effects of other medications (See the specific medication.)
- anaphylaxis (life-threatening allergic reaction)
Call for an appointment with your health care provider if severe symptoms of hay fever occur, if previously successful treatment has become ineffective, or if symptoms do not respond to treatment.
