2.1. Definition of atopy

The term “atopy” was first introduced by Coca and Cooke in the beginning of the 20^th century as reviewed by Wamboldt et al. (1998). Originally the term “atopy” meant “unusual” (Abbas et al. 2000), and Coca and Cooke meant with that an inherited tendency, which was associated with hay fever, asthma and urticaria (Nikander 1999). These disorders have been called atopic disorders even though nowadays it is known that, for example, the etiology of urticaria is heterogeneous and that all patients with asthma are not suffering from atopic allergies. In addition, atopic dermatitis is defined to be an atopic disorder even though it was not included in the original definition (Nikander 1999). In older epidemiological studies, positive skin tests, high immunoglobulin E (IgE) levels, and atopy were treated as synonymous (Wamboldt et al. 1998). Nowadays, persons, who have a tendency to produce IgE antibodies in response to various environmental antigens and who exhibit strong immediate hypersensitivity response, are called atopic. In different individuals, atopy may manifest itself in different forms – e.g., asthma, atopic dermatitis (eczema), allergic rhinitis and allergic conjunctivitis (Kari & Hannuksela 1999, Abbas et al. 2000, Wamboldt et al. 2000). In clinical practice the presence of atopy requires both positive skin tests and clinical symptoms (Wamboldt et al. 1998).