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THE MERCK MANUAL MEDICAL LIBRARY: The Merck Manual of Medical Information--Home Edition
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Seasonal Allergies

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Seasonal allergies result from exposure to airborne substances (such as pollens) that appear only during certain times of the year.

  • Seasonal allergies cause itchy skin, a runny nose, watery and bloodshot eyes, and sneezing,
  • Symptoms and their seasonal appearance usually suggest the diagnosis, and skin tests can help identify the allergy trigger.
  • Antihistamines, decongestants, and corticosteroid nasal sprays help relieve symptoms.

Seasonal allergies (commonly called hay fever) are common. They occur only during certain times of the year—particularly the spring, summer, or fall—depending on what a person is allergic to. Symptoms involve primarily the membrane lining the nose, causing allergic rhinitis, or the membrane lining the eyelids and covering the whites of the eyes (conjunctiva), causing allergic conjunctivitis (see Conjunctival and Scleral Disorders: Allergic Conjunctivitis).

The term hay fever is somewhat misleading because symptoms do not occur only in the summer when hay is traditionally gathered and never include fever. Hay fever is usually a reaction to pollens and grasses. The pollens that cause hay fever vary by season:

  • Spring: Usually trees (such as oak, elm, maple, alder, birch, juniper, and olive)
  • Summer: Grasses (such as Bermuda, timothy, sweet vernal, orchard, and Johnson grass) and weeds (such as Russian thistle and English plantain)
  • Fall: Ragweed

Also, different parts of the country have very different pollen seasons. In the western United States, mountain cedar (a juniper) is one of the main sources of tree pollen from December to March. In the arid Southwest, grasses pollinate for much longer, and in the fall, pollen from weeds, such as sagebrush and Russian thistle, can cause hay fever. People may react to one or more pollens, so their pollen allergy season may be from early spring to late fall. Seasonal allergy is also caused by mold spores, which can be airborne for long periods of time during the spring, summer, and fall.

Allergic conjunctivitis may result when airborne substances, such as pollens, contact the eyes directly.

Symptoms

Hay fever can make the nose, roof of the mouth, back of the throat, and eyes itch. Itching may start gradually or abruptly. The nose runs, producing a clear watery discharge, and may become stuffed up. In children, the stuffy nose may lead to an ear infection. The lining of the nose may become swollen and bluish red.

The sinuses may also become stuffed up, causing headaches. Sneezing is common.

The eyes may water, sometimes profusely, and itch. The whites of the eyes may become red, and the eyelids may become red and swollen. Wearing contact lenses can irritate the eyes further.

Other symptoms include coughing, wheezing, and irritability. A few people become depressed, lose their appetite, and have problems sleeping.

The severity of symptoms varies with the seasons.

Many people who have allergic rhinitis also have asthma (which results in wheezing), possibly caused by the same allergens that contribute to allergic rhinitis and conjunctivitis.

Diagnosis

The diagnosis is based on symptoms plus the circumstances in which they occur—that is, whether they occur only during certain seasons. This information can also help doctors identify the allergen.

The nasal discharge may be examined to see whether it contains eosinophils (a type of white blood cell produced in large numbers during an allergic reaction). Skin tests can help confirm the diagnosis and the identity of the allergen (see Allergic Reactions: Diagnosis).

Treatment

Nasal Symptoms: Antihistamines are usually used first (see Allergic Reactions: Antihistamines). Sometimes a decongestant, such as pseudoephedrine Some Trade Names
AFRINOLSUDAFED
, is taken by mouth with the antihistamine to help relieve a stuffy nose. Many antihistamine-decongestant combinations are available as a single tablet. However, people with high blood pressure should not take a decongestant unless a doctor recommends it and monitors its use. Nonprescription decongestant nose drops or sprays should not be used for more than a few days at a time because using them continually for a week or more may worsen or prolong nasal congestion. This reaction is called a rebound effect, which may eventually result in chronic congestion. Antihistamines may also have other side effects, particularly anticholinergic effects. They include sleepiness, dry mouth, blurred vision, constipation, difficulty with urination, confusion, and light-headedness.

A corticosteroid nasal spray is also effective. This spray may be prescribed instead of or in addition to antihistamines. Most of these sprays have few side effects, although they can cause nosebleeds and a sore nose.

Other drugs are sometimes useful. Cromolyn Some Trade Names
CROLOMINTAL
is available by prescription as a nasal spray and may help relieve a runny nose. To be effective, it must be used regularly. Azelastine Some Trade Names
OPTIVAR
(an antihistamine) and ipratropium Some Trade Names
ATROVENT
, both available by prescription as nasal sprays, may be effective. But these drugs can have anticholinergic effects similar to those of antihistamines taken by mouth, especially drowsiness.

Montelukast Some Trade Names
SINGULAIR
, a leukotriene modifier, reduces inflammation and helps relieve a runny nose. But how it is best used has not been established. Omalizumab Some Trade Names
XOLAIR
may be used when other treatments are ineffective. This drug binds to immunoglobulin E (IgE), an antibody produced in large amounts during an allergic reaction. Both montelukast Some Trade Names
SINGULAIR
and omalizumab Some Trade Names
XOLAIR
are available by prescription.

Regularly flushing out the sinuses with a warm water and salt (saline) solution may help loosen and wash out mucus and hydrates the nasal lining. This technique is called sinus irrigation.

When these treatments are ineffective, a corticosteroid may be taken by mouth or by injection for a short time (usually for fewer than 10 days). If taken by mouth or injection for a long time, corticosteroids can have serious side effects.

Eye Symptoms: Bathing the eyes with plain eyewashes (such as artificial tears) can help reduce irritation. Any substance that may be causing the allergic reaction should be avoided. Contact lenses should not be worn during episodes of conjunctivitis.

Eye drops containing antihistamines and a drug that causes blood vessels to narrow (a vasoconstrictor) are often effective. These eye drops are available without a prescription. However, they may be less effective and have more side effects that prescription eye drops (see Conjunctival and Scleral Disorders: Diagnosis and Treatment). Eye drops containing cromolyn Some Trade Names
CROLOMINTAL
, available by prescription, are used to prevent rather than relieve allergic conjunctivitis. They can be used when exposure to the allergen is anticipated. If symptoms are very severe, eye drops containing corticosteroids, available by prescription, may be used. During treatment with corticosteroid eye drops, the eyes should be checked regularly for increased pressure and infection by an ophthalmologist.

Allergen Immunotherapy: If other treatments are ineffective, allergen immunotherapy helps some people (see Allergic Reactions: Allergen Immunotherapy). Immunotherapy is needed in the following situations:

  • When symptoms are severe
  • When the allergen cannot be avoided
  • When the drugs usually used to treat allergic rhinitis or conjunctivitis cannot control symptoms
  • If asthma develops

Allergen immunotherapy for hay fever should be started after the pollen season to prepare for the next season. Immunotherapy has more side effects when started during pollen season because the allergens have stimulated the immune system. Immunotherapy is most effective when continued year-round.

Last full review/revision September 2008 by Peter J. Delves, PhD

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