Allergic rhinitis

Alternative names:

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).

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.