What is hay fever?

Causes and Symptoms

Allergic rhinitis, popularly known as hay fever, represents the most common allergic disorder, affecting approximately 10 percent of the population; the most common source of the allergy is wind-dispersed pollen. These tiny grains are produced in phenomenal numbers to ensure transfer of the pollen (which contains the plant’s sperm) to other flowers of the same plant species. Trees, grasses, and certain forbs (especially the ragweeds) are the most common culprits. The first time that a susceptible person is exposed, the pollen acts to sensitize the immune system. On second and subsequent exposures, the pollen triggers an allergic response.

This response is triggered by the formation of a specific class of antibody known as IgE against the proteins on the pollen grains (generally called antigens and in this case called allergens). Immunoglobulin E (IgE) attaches to tissue cells called mast cells by one end and to the pollen grains at the other end. This attachment causes the mast cells to release defensive substances, the best known of which is histamine. These substances cause increased permeability of capillaries and the production and release of mucous and watery substances from the nasal passages and eyes. Itching and sneezing accompany the release. The tendency to produce IgE against pollen allergens is an inherited trait; persons with one or both parents who have allergies to certain substances are more likely to exhibit the same allergies than persons whose parents do not exhibit such responses.

Treatment and Therapy

It is generally agreed that avoidance of the allergen is the most effective therapy for hay fever. Staying inside a building with air conditioning or well-filtered air during the worst allergy season helps. However, avoiding an allergen completely, such as ragweed pollen during ragweed’s flowering season, is essentially impossible.

The most common treatments employed are desensitization and drugs. Desensitization involves a series of injections of slowly increasing concentrations of the allergen, in the hope of turning the patient’s immune system from the production of IgE to the production of immunoglobulin G (IgG), which does not trigger the mast cells. Drugs such as antihistamines, which block the action or the release of histamine and the other substances released by mast cells, are commonly recommended, either in prescription strength or over the counter. Steroid and decongestant sprays have also been successful in relieving the symptoms of hay fever in some individuals.

Perspective and Prospects

For many persons, long-term avoidance of allergens such as pollen may be difficult. Current drugs such as antihistamines are directed primarily at relieving symptoms without removing the cause: the binding of IgE to the allergen. Future drugs may address the variety of steps involved in the allergic response while causing fewer side effects such as sleepiness. Other treatments may involve augmentation of IgG production in response to immunization with the allergen, since IgG competes with IgE in binding to the allergen.

Bibliography

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Carson-DeWitt, Rosalyn. "Allergic Rhinitis." Health Library, October 31, 2012.

Delves, Peter J., et al. Roitt’s Essential Immunology. 12th ed. Malden, Mass.: Blackwell, 2011.

"Hay Fever." Mayo Clinic, July 17, 2012.

Janeway, Charles A., Jr., et al. Immunobiology: The Immune System in Health and Disease. 6th ed. New York: Garland Science, 2005.

Owen, Judy, Jenni Punt, and Sharon Stranford. Kuby Immunology. 7th ed. New York: W. H. Freeman, 2013.

Rabson, Arthur, et al. Really Essential Medical Immunology. 2d ed. Malden, Mass.: Blackwell Science, 2005.