A Cochrane review ¹ included 88 studies with a total of 3,792 subjects (3459 with asthma). Of the trials 42 were of immunotherapy for house mite allergy, 27 for pollen allergy, 10 for animal dander, 2 Cladosporium mould allergy, 2 latex and six trials looking at multiple allergens. Overall, there was a significant reduction in asthma symptoms and medication and improvement in bronchial hyper-reactivity following immunotherapy. There was a significant improvement in asthma symptom scores (standardised mean difference –0.59, 95% CI –0.83 to –0.35). NNT to avoid one deterioration in asthma symptoms was 3 (95% CI 3 to 5) and to avoid one requiring increased medication NNT was 4 (95% CI 3 to 6). Allergen immunotherapy significantly reduced allergen specific bronchial hyper-reactivity, with some reduction in non-specific bronchial hyper-reactivity as well. There was no consistent effect on lung function. If 16 patients were treated with immunotherapy, one would be expected to develop a local adverse reaction. If nine patients were treated with immunotherapy, one would be expected to develop a systemic reaction (of any severity).