Hay Fever

Hay Fever
(Allergic Rhinitis)

Common Allergy Triggers Slideshow

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

• What is hay fever? What are the symptoms and signs?
• Why does an allergic reaction occur?
• What causes allergic rhinitis?
• When and where does allergic rhinitis occur?
• How is allergic rhinitis diagnosed, and how are allergies identified?
• How are allergies treated?
• Hay Fever At A Glance
• Pictures of Common Allergy Triggers - Slideshow

Hay fever affects up to 30% of all Americans, including up to 40% of children and 10%-30% of adults. Over $1 billion is spent each year in this country to treat this disorder, and millions of school and work days each year are lost by sufferers of hay fever symptoms. These figures are probably an underestimate because many of those affected may attribute their discomfort to a chronic cold. Although childhood hay fever tends to be more common, this condition can occur at any age and usually occurs after years of repeated inhalation of allergic substances. The incidence of allergic disease has dramatically increased in the U.S. and other developed countries over recent decades.

What is hay fever? What are the symptoms and signs?

Hay fever is a misnomer. Hay is not a usual cause of this problem, and it does not cause fever. Early descriptions of sneezing, nasal congestion, and eye irritation while harvesting field hay promoted this popular term. Allergic rhinitis is the correct term used to describe this allergic reaction, and many different substances cause the allergic symptoms noted in hay fever. Rhinitis means "irritation of the nose" and is a derivative of rhino, meaning nose. Allergic rhinitis which occurs during a specific season is called "seasonal allergic rhinitis." When it occurs throughout the year, it is called "perennial allergic rhinitis."

Symptoms of allergic rhinitis, or hay fever, frequently include nasal congestion, a clear runny nose, sneezing, nose and eye itching, and excess tear production in the eyes. Postnasal dripping of clear mucus frequently causes a cough. Loss of the sense of smell is common, and loss of taste sense occurs occasionally. Nose bleeding may occur if the condition is severe. Eye itching, redness, and excess tears in the eyes frequently accompany the nasal symptoms. The eye symptoms are referred to as "allergic conjunctivitis" (inflammation of the whites of the eyes). These allergic symptoms often interfere with one's quality of life and overall health.

Allergic rhinitis can lead to other diseases such as sinusitis and asthma. Many people with allergies have difficulty with social and physical activities. For example, concentration is often difficult while experiencing allergic rhinitis.

Why does an allergic reaction occur?

An allergic reaction occurs when the immune system attacks a usually harmless substance called an allergen that gains access to the body. To more simply describe this complex immune process, we will make an analogy to a war within the body. The immune system calls upon a protective substance called immunoglobulin E (IgE) antibodies ("E" for "erythema" or redness) to fight these invading allergic substances or allergens. Even though everyone has some IgE, an allergic person has an unusually large army of these IgE defenders -- in fact, too many for his/her own good. This army of IgE antibodies attacks and engages the invading army of allergic substances of allergens.

As is often the case in war, innocent bystanders are affected in battle. These innocent bystanders are special cells called mast cells. These cells are frequently injured during the warring of the IgE antibodies and the allergic substances. When a mast cell is injured, it releases a variety of strong chemicals into the tissues and blood, one of which is known as histamine. These chemicals frequently cause allergic reactions. These chemicals are very irritating and cause itching, swelling, and fluid leaking from cells. Through various mechanisms, these allergic chemicals can cause muscle spasm and can lead to lung and throat tightening as is found in asthma and loss of voice.