Grass-pollen-induced allergic rhinoconjunctivitis (or hay fever as it is generally called by patients) is a common clinical problem among children and young adults. The symptoms are fairly stereotyped and include itching and redness of the eyes, itchy nose, watery rhinorrhoea and nasal congestion. Sometimes there is mild chest tightness, especially in those with an underlying asthmatic tendency. In addition, many sufferers complain of systemic symptoms, such as tiredness and irritability, although these may be partially due to the side effects of medication, particularly oldergeneration antihistamines. Hay fever is often mild and thesymptoms can be controlled by simple measures, such as antihistamines used as required. A minority of patients have more severe symptoms, which may respond to regular prophylactic treatment with intranasal corticosteroids. However, these treatments are not always effective. In a questionnaire survey of UK patients with grass pollen hay fever who were all receiving regular antihistamines and intranasal steroid sprays, about 30% reported poor symptom control, especially of the systemic symptoms. In many countries, such patients would be offered desensitisation, but this is not uniformly available.

Specific Allergen Immunotherapy
Specific allergen immunotherapy (SIT) involves the administration of allergenic molecules or extracts to modify or abolish the symptoms of atopic allergic disease. The key features of SIT are that it offers a long-term reduction in symptoms, but its effects are confined to the allergen that is given. Therefore, before starting a patient on SIT it is essential to make an accurate diagnosis in order to identify relevant trigger factors and also to have tried appropriate avoidance strategies. If allergen avoidance and simple drug therapy enable satisfactory control of symptoms, it may be difficult to justify giving SIT. However, drug treatments only work for as long as they are taken, so there can be a case for SIT even in patients who achieve adequate control with medication. Conversely, if the patient’s symptoms appear to be driven by a variety of allergic triggers, it is unlikely that SIT directed against a single allergen will improve the situation. Therefore, each patient needs to be assessed individually and given appropriate, tailored advice.

SIT was developed by Noon and Freeman, from St Mary’s Hospital, London, and published almost 100 years ago.1 In conventional SIT, which still follows the principles of Noon and Freeman, treatment is started with a low dose of allergen and the dose is then increased, usually at weekly intervals over about three months, until the maintenance dose is achieved. Maintenance doses can then be given at four- to six-weekly intervals for the maintenance period, which is typically three years. Sometimes patients cannot tolerate the full maintenance dose due to side effects, in which case the maximum tolerated dose is given instead. Shorter regimes, given each year just before the pollen season, may offer comparable levels of benefit, at least in the short term. Whichever regime is used, the benefit is partial, with patients continuing to experience some symptoms, although usually much less than before their SIT. In recent years, there has been considerable interest in alternative routes of administration, especially sublingual immunotherapy.

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