It is of great concern, that allergic diseases are increasing and moving to younger age categories. Since the highest incidence of allergic diseases has been found in populations of industrially developed countries, recent research turns its attention not only to the genetic factors, but also to the role of environmental factors in allergy development. This research is highly topical, as only by comprehension of the mechanism of allergy development preventive measures can be proposed. The ongoing research studies in Slovakia with cohorts of mothers and their children at the age of 1 to 5 years showed original results, when incidence of allergic diseases in children varied in relation to the predominating type of the environmental pollution in a region. Some results are discussed with more details, such as the monitoring of mother’s exposure to xenobiotics during pregnancy in relation to allergic sensitization.