Asthma is one of the most common chronic diseaseworldwide, affecting almost 300 million people with a1continuously increasing prevalence . It is also the mainchronic disease in childhood, affecting 10% of children. Agreat effort is currently being focused on the search ofpreventive strategies, which seems feasible based onevidence suggesting that the onset of atopy and asthmamay be strictly connected to several events occurring invery early stages of life. In particular, exposure to2antibiotics in fetal and neonatal period , being born by3cesarean section , formula feeding, maternal diet, and the variety of microbes one is exposed to may play a key role.