On exposure to the allergen, the patient is sensitized and the white blood corpuscles release histamine and other materials involved in an inflammation reaction. This causes swelling of the nasal mucous membrane, the patient’s eyes smart and run, he sneezes and his nose streams. Grass pollen is not present throughout the year and for this reason the complaint is seasonal, mostly confined to May in northern latitudes. The blocked nose may cause the patient to sleep badly, and the perpetual sneezing is also tiring. The complaint increases the chance of sinusitis and middle ear infection; nasal polyps are another possible complication. The blockage also raises the possibility of bacterial infection, and later susceptibility to asthma. Diagnosis is made from a description of the symptoms by the patient. On examination the doctor finds the nasal mucous membrane pale and swollen, the eyes are often red and a blood test shows increased IgE content. Skin tests can be used to identify the grass responsible: a highly diluted solution of various allergens is injected into the skin; if the patient is allergic, redness and swelling occur around the injected area after 15 to 20 minutes. Treatment then consists of avoiding the allergen, for example by installing air-conditioning and keeping windows and doors closed in the pollen season. Holidays should also be timed to avoid the pollen. The publication of pollen counts also helps to provide a warning. De-sensitization injections can be given by administering increased doses of the allergen before the season begins, but only in the case of pollen allergy; not all patients benefit from it. The aim of the injections is to stimulate other parts of the immune system, thus preventing an escalating allergic reaction. Treatment is by medication. Corticosteroids in nasal sprays check the allergic reaction; used locally they have few side-effects, and should be used regularly throughout the season in small doses. Antihistamines suppress the allergic reaction, with the disadvantage of causing drowsiness. Sodium chromoglycate checks the release of histamines, but must be used throughout the season to be effective. It does not cause drowsiness.