HAYFEVER

Skin prick tests can help identify what substance a sufferer is allergic to.

There is evidence the prevalence of hayfever is increasing.

What is hay fever?

The hallmark of hayfever is the relationship of symptoms on exposure to an allergen. Your nose is not the only organ that may be affected in hayfever. You may also have itching of your eyes (allergic conjunctivitis), throat and ears.

Seasonal allergic rhinitis (hay fever) symptoms are experienced only during spring and/or summer. It is usually due to various types of pollen, which are carried by the wind and easily breathed into the nose. When most people talk about hay fever it usually means seasonal allergic rhinitis.

What is the mechanism of hayfever?

Allergic rhinitis is a hypersensitivity response to specific allergens in sensitised patients that are mediated by IgE antibodies. Sensitised patients with allergic rhinitis have IgE antibodies for specific allergen(s) bound to receptors on the surface of mast cells. On re-exposure to the specific allergen(s), cross-linking of adjacent IgE molecules occurs, and mast cell degranulation (rupture) takes place, releasing a variety of chemical mediators that may be performed (histamine) or newly synthesized (leukotrienes, prostaglandins).

Histamine causes the cardinal symptoms of allergic rhinitis including sneezing, nasal itching, and runny nose. The nasal congestion is more due to leukotrienes than to histamine. Hence antihistamines are not very good at relieving nasal congestion.

A large number of patients with allergic rhinitis will have an increase in sensitivity to allergens after repeated daily exposure; an effect called "priming". At the start of the pollen season, comparatively large doses of pollens are needed to trigger an allergic response but toward the middle and end of the season, patients become extremely reactive to even small amounts of pollen.

How is hayfever diagnosed?

The history: It should be ascertained whether the allergic symptoms are seasonal or perennial. The exact month of the year that symptoms start could give a clue as to the specific type of pollen involved.

The tree pollen season starts in late winter and usually ends before the grass pollen season in spring. The weed pollen season overlaps with the grass season, usually starting in late spring and extending through to end of summer.

Skin prick test should be performed to identify the specific allergen(s) involved, so that the correct avoidance measures can be recommended. The skin prick test is a sensitive, simple and cheap diagnostic technique.

How is hay fever treated?

Broadly speaking there are three main options in the treatment of hayfever (seasonal allergic rhinitis).

1. Avoiding allergens

Total eradication of the allergen is usually not possible, but measures to reduce exposure to the allergen in the local environment should be encouraged.

Pollen:

Pollen particles are part of the reproductive mechanism of plants and are an environmental contaminant, which are difficult or impossible to eliminate. Measures, which can help to reduce the exposure, include:

- Keep windows in cars and buildings shut
- Wear glasses or sunglasses
- Avoid open grassy places, particularly in the evening and at night
- Use a car with a pollen filter
- Check the pollen count in the media
- During the peak season take your holidays by the sea or abroad

2. Drug treatment

Patients may need drugs for hayfever if avoiding the allergen is impossible or fails to control the symptoms.

In recent years, the mainstay of treatment for seasonal allergic rhinitis has been the use of topical corticosteroid nasal sprays and non-sedating antihistamines. These may be highly effective when used, either alone or in combination.

Antihistamines and decongestants simply relieve symptoms.

Topical decongestants should not be used for more than 5 days because of rebound congestion.

3. Immunotherapy

Immunotherapy is the injection of increasing doses of the identified allergen(s), in order for the body to build up a resistance to it.

Hayfever may, in general, be effectively managed with a combination of allergen avoidance measures plus topical corticosteroids and oral non-sedating antihistamines.

There remains a small group of subjects who, despite regular use of medication, continue to have marked symptoms or unacceptable side-effects from their medication. These patients should be offered immunotherapy.