Use of antibacterials in infancy: clinical implications for childhood asthma and allergies.

Evidence from experimental studies in rodents and results from epidemiologic studies with a retrospective design suggest a possible causal association between antibacterial use in early childhood and asthma. Such an association is thought to be mediated by antibacterial-induced alterations in the intestinal flora, leading to a skewing of the immune system of young children toward an atopic phenotype. However, results from recently conducted prospective studies suggest that the previously observed association between antibacterial use in early childhood and asthma is not one of 'cause and effect' but rather that frequent antibacterial use in early childhood may be a marker of an increased risk of being diagnosed with asthma later in childhood. Although antibacterials should not be used excessively in young children, their use in early childhood is not likely to explain the increased prevalence of asthma and allergies in children in industrialized countries.