Allergic rhinitis is a collection of symptoms, predominantly in the nose and eyes, caused by airborne particles of dust, dander, or plant pollens in people who are allergic to these substances.

When these symptoms are caused by pollen, the allergic rhinitis is commonly known as "hay fever".

See also:

• allergies
• allergy to mold, dander, dust
• asthma

Allergies are caused by an oversensitive immune system, leading to a misdirected immune response. The immune system normally protects the body against harmful substances such as bacteria and viruses. Allergy occurs when the immune system reacts to substances (allergens) that are generally harmless and in most people do not cause an immune response.

As noted above, hay fever 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. Large, visible pollens are seldom responsible for hay fever. Tiny, hard to see pollens 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 when most 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. When the antibodies are stimulated by pollen and dust, histamine (and other chemicals) are released. This causes itching, swelling, and mucus production. Symptoms vary in severity from person to person. Very sensitive individuals can experience hives or other rashes.

Some disorders may be associated with allergies. These include eczema and asthma, among others.

Allergies are common. Heredity and environmental exposures may contribute to a predisposition to allergies.

• coughing
• headache
• itching nose, mouth, eyes, throat, skin, or any area
• runny nose
• Impaired smell
• sneezing
• stuffy nose (nasal congestion)
• tearing eyes
• sore throat
• wheezing

The history of the person's symptoms is important in diagnosing allergic rhinitis, including whether the symptoms vary according to time of day or the season; exposure to pets or other allergens; and diet changes.

Allergy testing may reveal the specific allergens the person is reacting to. Skin testing is the most common method of allergy testing. This may include intradermal, scratch, patch, or other tests. Less commonly, the suspected allergen is dissolved and dropped onto the lower eyelid as a means of testing for allergies. (This test should only be done by a physician, never the patient, since it can be harmful if done improperly.)

In certain individuals who cannot undergo skin testing (as determined by the doctor), the RAST blood test may be helpful in determining specific allergen sensitivity.

The goal of treatment is to reduce allergy symptoms caused by the inflammation of affected tissues.

The best "treatment" is to avoid what causes your allergic symptoms in the first place. (See Prevention, below.) It may be impossible to completely avoid all allergens to which you are sensitive, but you can often take steps to reduce exposure.

Medication options include the following:

• Short-acting antihistamines, which are generally over-the-counter (non-prescription), often relieve mild to moderate symptoms, but can cause drowsiness. A pediatrician should be consulted before using these medicines in children, as they may affect learning. One formerly prescription medication, loratadine (Claritin), is now available over the counter. It does NOT tend to cause drowsiness or affect learning in children.
• Longer-acting antihistamines cause less drowsiness, can be equally effective, and usually do not interfere with learning. These medications, which require a prescription, include fexofenadine (Allegra), and cetirizine (Zyrtec).
• Nasal corticosteroid sprays are very effective and safe for people with symptoms not relieved by antihistamines alone. These prescription medications include fluticasone (Flonase), mometasone (Nasonex), and triamcinolone (Nasacort).
• Decongestants may also be helpful in reducing symptoms such as nasal congestion, but should not be used for long periods.
• Cromolyn sodium is available as a nasal spray (Nasalcrom) for treating hay fever. Eye drop versions of cromolyn sodium and antihistamines are available for itchybloodshot eyes.

The most appropriate medication depends on the type and severity of symptoms. Specific illnesses that are caused by allergies (such as asthma and eczema) may require other treatments.

Allergy shots (immunotherapy) are occasionally recommended if the allergen cannot be avoided and if symptoms are hard to control. This includes regular injections of the allergen, given in increasing doses (each dose is slightly larger than the previous dose) that may help the body adjust to the antigen.

Most symptoms of allergic rhinitis can be readily treated.

In some cases (particularly children), people may outgrow an allergy as the immune system becomes less sensitive to the allergen. However, as a general rule, once a substance causes allergies for an individual, it can continue to affect the person over the long term.

More severe cases of allergic rhinitis require immunotherapy (allergy shots) or removal of tissue in the nose (e.g., nasal polyps) or sinuses.

• drowsiness and other side effects of antihistamines
• side effects of other medications (see the specific medication)
• sinusitis
• nasal polyps
• disruption of lifestyle (usually not severe)

Symptoms can sometimes be prevented by avoiding known allergens. During the pollen season, people with hay fever should remain indoors in an air-conditioned atmosphere whenever possible:

• Most trees produce pollen in the spring
• Grasses and flowers usually produce pollen during the summer
• Ragweed and other late-blooming plants produce pollen during late summer and early autumn.

For people who are sensitive to certain indoor allergens, dust mite covers for mattresses and pillowcases are recommended, as well as avoiding culprit pets or other triggers.