Unité de toxicologie Université catholique de Louvain Avenue Mounier 53 Bte 53.02 B-1200 Bruxelles Belgique
Human exposure to chlorination products has markedly increased during the 20th century, first with the chlorination of drinking water and later, beginning in the 1960s, with the development of public and private swimming pools. Studies in Belgium, supported by observations made in Norway, Germany and the Netherlands, suggest that chlorination products in indoor and outdoor swimming pools act as chemical adjuvants that promote the development of allergic diseases including asthma, hay fever and allergic rhinitis. In subjects sensitized against airborne allergens or with higher serum IgE levels, the relative risk of asthma rises by 1 to 2% for each hour spent in a chlorinated swimming pool — indoors or out. These findings have led to the “chlorine hypothesis”, which proposes that the rise of allergic diseases in the developed world results less from the greater levels of hygiene (“hygiene hypothesis”) than from the increasing and largely uncontrolled exposure of children to chlorination products used for swimming pool disinfection.