The study, published in the journal Chest, looked at the medical histories of 13,116 children from birth to age 7.
Two-thirds were given an antibiotic before their 1st birthday.
Researchers found they were far more likely to have asthma than those not given the drugs – and the more courses of antibiotics they were given, the greater the chances.
When the scientists excluded those given antibiotics for breathing problems – who might be expected to have a higher chance of developing asthma – the connection appeared even stronger.
Asthma in 7 year olds was nearly twice as likely in children given an antibiotic for a nonrespiratory tract infection than in children who had been given no antibiotics at all.