Ency. home > Disease > A > Allergic rhinitis

Allergic rhinitis   

Overview | Symptoms | Treatment | Prevention

Alternative names:

Hay fever; Nasal allergies

Definition:

A collection of symptoms, predominantly in the nose and eyes, that occur after exposure to airborne particles of dust or dander or to pollens of certain seasonal plants in people that are allergic to these substances (see also allergies; asthma; allergy to mold, dander, dust).

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 geographic differences in local plant populations, 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 or dust is inhaled by a person with a sensitized immune system, it triggers antibody production; these antibodies bind to cells that contain histamine. Histamine (and other chemicals) are released by these cells when the antibodies are stimulated by allergens. This causes itching, swelling of affected tissues, mucus production, muscle spasms, hives, rashes, and other symptoms. Symptoms vary in severity from person to person.

Some disorders may be associated with allergies in general, and allergic rhinitis in particular. These include eczema and asthma, among others.

Allergies are common. Heredity, environmental conditions, and number and type of exposures may contribute to a predisposition to allergies.

Ency. home > Disease > A > Allergic rhinitis

[an error occurred while processing this directive]