Allergy is defined as a hypersensitivity reaction due to specific antibody-mediated or cell-mediated immunologic mechanisms. Epidemiological studies are showing a dramatic increase of allergies in industrialized countries in the last few decades, while remaining stable in developing countries. In 1989 Strachan, hypothesized that the increase in allergic disorders was the result of a lack of infections in early infancy, and in 1998 Wold suggested that, rather than a decrease in viral or bacterial infections, an altered normal intestinal colonization pattern in infancy, could be responsible for the increase in allergies. Germ-free mice were shown to mount an exaggerated allergic airway reaction compared with that seen in colonized mice, indicating the important role of microbe-host interactions in the development of allergic diseases. Infants with food allergies are found to exhibit an imbalance between "beneficial"and potentially harmful bacteria, i.e., decreased Lactobacilli, Bifidobacteria and Enterococcus species and increased coliforms, Staphylococcus aureus and Clostridium species, suggesting that microbial inhabitants of the human body, may play either a pathogenic or protective role in allergies. Based on this data, many clinical trial addressing the use of probiotics in the context of allergic disorders, have been conducted in children. However, currently, no conclusive item may be drawn.