Hay fever, or seasonal allergy, is a type of allergic rhinitis * caused by an allergic reaction to plant pollens. In the United States the most common causes of hay fever are ragweed, tree, or grass pollen.
Hay fever is one of several allergies * that are called atopy * or atopic (a-TOP-ik) allergies because they affect parts of the body that are not in direct contact with the allergens * . About 20 percent of people with hay fever eventually develop asthma, and some develop eczema * as well. Doctors refer to hay fever as allergic rhinitis because it involves irritation and inflammation of the nasal passages. Hay fever may be seasonal, meaning that the person has a runny nose and other symptoms only during certain periods of the year, or perennial, which means that the person has symptoms all year long. Other names for hay fever are grass fever and rose fever.
Hay fever is very common in the United States. The National Institutes of Health estimates that between 20 and 25 percent of Americans have some form of hay fever, although the specific pollens that trigger the symptoms vary from region to region across the United States. In general, the hay fever season is shorter in the northern states and longer in the South, particularly along the East Coast. The pollen count is highest in most parts of the country from mid-spring to early summer.
The most common sources of the pollens that trigger hay fever are plants or trees that are pollinated by the wind rather than by bees or other insects. Such trees and other plants include birch, alder, willow, and horse chestnut trees; ryegrass, Kentucky bluegrass, timothy grass, and Bermuda grass; and ragweed, sorrel, and sagebrush.
Hay fever affects children more often than adults. About 80 percent of people with hay fever develop it before the age of 20 years, with the average age at the time of the first episode being between 8 and 11 years of age. Some doctors think that as many as 40 percent of children may suffer from hay fever at some point in childhood. The symptoms typically become less severe in adulthood and may go away completely.
The most noticeable symptoms of hay fever are a stuffy or runny nose, sneezing, and teary or watery eyes. Some people also have coughing, headaches, fatigue, and drowsiness. These symptoms are easily confused with the symptoms of a cold. Unlike colds, hay fever is not contagious. However, it does appear to run in families. It is possible for several members of a family to be affected by hay fever at the same time if they are all allergic to the same type of weed or tree pollen, but this fact does not mean that the disorder can be spread from one person to another like a cold.
Many people who get the runny nose, watery eyes, and other symptoms of hay fever think at first that they just have a cold. One way to tell the difference is that colds usually clear up in about a week. Another difference is that hay fever is usually worse during certain months of the year or at certain times of day during pollen season. Hot, dry, and windy days are more likely to trigger the symptoms of hay fever than cool or rainy days. The pollen count is also more likely to be higher early in the morning than later in the day. The symptoms of hay fever are not caused by viruses like those that cause colds. They develop when plant or weed pollen enters the person's airway and the tissues that line the eyelids. Then white blood cells in the immune system * produce antibodies * to the plant allergens. These antibodies are stored in special cells in the mucous membranes lining the nose and eyelids known as mast cells. When the allergen comes in contact with the mast cells, a compound called histamine * is released. Histamine is responsible for the runny nose, itchy and watery eyes, and sneezing of hay fever.
The first step in diagnosing hay fever is to take a history of the patient's symptoms. The doctor will ask when the symptoms began; whether they appear during the same time of year every year; whether the symptoms are continuous or come and go; and whether they are worse at specific times of day. In most cases, the doctor will ask whether there is a family history of allergies and whether the patient also has asthma or eczema.
The next step is a series of skin tests to find out which specific pollens are causing the patient's runny nose and other symptoms. The doctor takes a small amount of material extracted from a specific type of pollen and injects it under the patient's skin or applies it to a tiny scratch on the arm or upper back. If the patient is allergic to the material, the skin will develop a wheal, or flat-topped reddish swelling.
There are three parts to treating hay fever: avoiding the specific trigger(s); using medications to relieve such symptoms as itching eyes and a runny nose; and taking allergy shots to reduce one's sensitivity to triggers.
The doctor may recommend one or more of the following types of medications in treating hay fever:
The most common strategy for preventing hay fever is avoiding the plants that trigger the patient's symptoms. Staying indoors when the pollen count is high, filtering the air inside the house, avoiding grassy fields or large forested areas, or moving to a part of the country with a dry desert climate are some ways people lower their exposure to airborne pollens.
Another approach is desensitization *
A possibility for preventing hay fever is a vaccine * that was being tested in patients in Canada, Europe, and the United States in 2015.
See also Allergies • Asthma • Sinusitis
De Lange, Catherine. “Mix of Hepatitis and Pollen Blows Hay Fever Away.” New Scientist, December 31, 2013. https://www.newscientist.com/article/mg22129504.100-mix-of-hepatitis-and-pollen-ws-hay-fever-away (accessed July 15, 2015).
Lee, Stella. “Allergic Rhinitis (Hay Fever).” American Rhinologic Society. http://care.american-rhinologic.org/allergic_rhinitis (accessed July 15, 2015).
National Asthma Council Australia. “Allergic Rhinitis (Hay Fever) and Your Asthma.” http://www.nationalasthma.org.au/uploads/publication/allergic-rhinitis-hay-fever-and-your-asthma.pdf (accessed July 15, 2015).
American Academy of Allergy, Asthma, and Immunology. 555 E. Wells St., Suite 1100, Milwaukee, WI 53202-3823. Telephone: 414-272-6071. Website: http://www.aaaai.org (accessed July 15, 2015).
National Institute of Allergy and Infectious Diseases. Office of Communications and Government Relations, 5601 Fishers Lane, MSC 9806, Bethesda, MD 20892-9806. Telephone: 301-496-5717. Toll-free: 866-284-4107. Website: http://www.niaid.nih.gov (accessed July 15, 2015).
* rhinitis (rye-NYE-tis) is the medical term for inflammation of the tissues inside the nose.
* allergies (AL-uhr-jeez) are immune system–related sensitivities to certain substances, for example, cat dander or the pollen of certain plants, that cause various reactions, such as sneezing, runny nose, wheezing, or swollen, itchy patches on the skin, called hives.
* atopy (AT-uh-pee) is an allergic hypersensitivity that affects parts of the body not in direct contact with the allergen, such as hay fever, asthma, or eczema.
* allergens are substances that provoke a response by the body's immune system or cause a hypersensitive reaction.
* eczema (EG-ze-mah) is an inflammatory skin condition characterized by redness, itchiness, and oozing blisters that become crusty and hard.
* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.
* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.
* histamine (HIS-tuh-meen) is a substance released by the body during inflammation. It causes blood vessels to expand and makes it easier for fluid and other substances to pass through vessel walls.
* desensitization (de-sens-ihtih- ZAY-shun) is a method for reducing a person's reaction to an allergen.
* vaccine (vak-SEEN) is a preparation of killed or weakened germs, or a part of a germ or product it produces, given to prevent or lessen the severity of the disease that can result if a person is exposed to the germ itself. Use of vaccines for this purpose is called immunization.