Antibiotic use in infancy disrupts gut microflora during a critical period for immune system development. It is hypothesized that this could predispose to the development of allergic diseases. A recent study found that children who were given antibiotics during infancy were at higher risk of developing asthma, eczema and hay fever by mid-childhood, compared to children who did not take antibiotics during infancy. The researchers concluded that the risk was associated with the total amount of antibiotic cycles taken during the first two years of life. Researchers investigated the associations of antibiotic use in the first 2 years of life with the development of asthma, eczema or hay fever by age 7.5  in a longitudinal birth cohort. Subjects were 4952 children from the Avon Longitudinal Study of Parents and Children (ALSPAC). Child antibiotic use and asthma, eczema and hay fever symptoms were maternally reported. Atopy was assessed by skin prick tests at age 7.5. The total number of antibiotic courses was considered as the main exposure. Data were analyzed using multivariate logistic regression. Children reported to have taken antibiotics during infancy (0–2 yr) were more likely to have asthma at 7.5 years, and the odds increased with greater numbers of courses. Increased antibiotic use was also associated with higher odds of eczema and hay fever but not atopy. The effect appeared to be associated with cumulative rather than a critical period of exposure during the first 2 yr. More information is available here.