For the play, see Hay Fever.

Pollen grains from a variety of common plants can cause hay fever.

Allergic rhinitis, also called pollinosis, hay fever or nasal allergies, is a collection of symptoms, predominantly in the nose and eyes, that occur after exposure to airborne particles of dust, dander , or the pollens of certain seasonal plants in people who are allergic to these substances.

When these symptoms are caused by pollens, the allergic rhinitis is commonly known as "hay fever", after the fact it is most prevalent during haying.

Causes

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. This is often exaggerated in populated areas (cities) where the female to male ratio of plants can frequently reach 9|1 or 10|1 (because male plants typically do not produce the clutter (fruit) that is consequent in female plants.) Subsubstances such as pollution and manmade chemicals, (chlorine, detergents, etc.) which can normally be tolerated can greatly aggrevate the condition.

The pollens that cause hay fever vary from person to person and from region to region, but generally speaking the tiny, hardly visible pollens of wind-pollinated plants are the predominant culprits. Pollens of insect-pollinated plants are too large to remain airborne and pose no risk. Examples of plants commonly responsible for hay fever include:

• Trees such as birch, alder, horse chestnut, hazel, willow, poplar, linden (birch is the most common culprit: 15-20% of people suffering from hay fever are allergic to birch pollen)
• Grasses (Gramineae), especially rye and timothy
• Wind-pollinated flowers (e.g. daisies)
• Weeds (e.g. ragweed, plantains, nettles, mugwort, sorrel)

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.

Symptoms

• 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
• cross-reactivity allergy to certain fruits

Signs and tests

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.

Sufferers might also find that cross-reactivity occurs. For example, someone alergic to birch pollen may also find that they have an allergic reaction to the skin of apples or potatoes. A clear sign of this is the occurrence of an itchy throat after eating an apple or sneezing when peeling potatoes. This occurs because of similarities in the proteins of the pollen and the food. There are many cross-reacting substances.

Treatment

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.

Medication

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.

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 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 itchy, bloodshot eyes.
• 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.

Expectations

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.

Complications

• 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)

External links

• NIH site on Allergic Rhinitis
• Hay Fever and Rhinitis - National Asthma Campaign (UK)
• Cross-Reactivity Allergies
• eMedicine Health