Asthma is most commonly found in athletes performing endurance events, such as cross-country skiing, swimming or long-distance running. Mild asthma (defined usually as increased BHR and asthma symptoms) is most common in endurance athletes, such as cross-country skiers (14–55%) [2, 3], swimmers (13–44%) [13, 17, 18, 20] and long- distance runners (15–24%) [13, 21]. Also, speed and power athletes, e.g. ice hockey players (15–19%) [6, 7, 8], and track and field athletes (16%) [13, 19], have a somewhat increased risk of asthma. Atopy as a risk factor Evidence for an increase in immunoglobulin E-mediated allergy has been shown in the general population [22, 23]. It seems that an increasing proportion of young athletes are atopic [8, 13] and suffer from symptoms caused by inhalant allergens. Hay fever, the most clear-cut atopic condition, is more common in summer sports athletes than in control subjects [13, 24]. Atopic disposition is a major risk factor along with the type of training. Risk of asthma is closely associated with atopy and its severity amongst athletes. When the risk factors "sporting event" and "atopy" were combined in a logistic regression model, the relative risk of asthma was surprisingly large: 25 fold in atopic speed and power athletes, 42 fold in atopic long-distance runners, and 97 fold in atopic swimmers compared with nonatopic control subjects [13]. Outcome of asthma and asthma-like symptoms Outcome of asthma in athletes has not been widely studied. In swimmers who stopped intensive training, BHR and asthma attenuated or even disappeared, whilst symptoms increased and eosinophilic airway inflammation was aggravated in swimmers who remained active during the 5-yr follow-up, irrespective of asthma treatment [18]. Thus, asthma in athletes is at least partly reversible, and intensive training seems to cause airway inflammation and asthmatic symptoms in susceptible individuals. Summary Clinical asthma, exercise-induced bronchospasm and bronchial hyperresponsiveness are more common in competitive athletes compared with the general population. Various atopic conditions (e.g. pollen allergy) seem to be more common in summer sports athletes thanincontrolsubjects.Typeoftrainingandatopyaremajorriskfactorsforlowerairway symptoms. Asthma is most commonly found in athletes performing endurance events, such as cross-country skiing, swimming or long-distance running. These athletes are repeatedly and strongly exposed to cold air and many inhalant irritants and allergens all year long. In symptomatic athletes, a mixed type of eosinophilic and neutrophilic airway inflammation often occurs leading in some individuals to functional abnormalities. Asthmatic symptoms in athletes areusually mildandat leastpartly reversible as they may disappear in those who stop intensive training. Keywords: Allergy, asthma, bronchospasm, bronchial hyperresponsiveness, epide- miology, exercise. ASTHMA, ALLERGY AND BHR IN SPORTS 3