They found that children under one treated with antibiotics were twice as likely as untreated children to develop childhood asthma.
The researchers carried out a meta-analysis of eight studies, including a total of 12,082 children, looking at the association between exposure to at least one course of antibiotics and development of childhood asthma.
They found that children exposed to antibiotics were more than twice as likely to be diagnosed with asthma in childhood as those not given antibiotics. The association was stronger in the four retrospective studies than in the four prospective ones.
The researchers then analysed a further five studies, including a total of 27,167 children, looking at the dose-response relationship between antibiotic exposure and development of asthma.
They found that the chance of developing asthma increased by 16 per cent for every course of antibiotics taken in the first year of life, although, again, the effect was stronger in retrospective than prospective studies.
Lead researcher Dr Carlo Marra, from the faculty of pharmaceutical sciences at the University of British Columbia, in Vancouver, said that the results supported reducing antibiotic prescribing to infants.
'Most antibiotics prescribed to children under four are for otitis media, URTIs and bronchitis,' he said. 'The latter two are mostly viral, and even for otitis media I would advocate not treating with antibiotics unless the child has very bad infection.'
Dr Marra said that the association between exposure to antibiotics and asthma fitted in with the hygiene hypothesis: 'Children who are exposed to more microbes have their immune systems develop more tolerance for the irritants that cause asthma.'
However, he added that the study did not prove that antibiotics were causing asthma.
'It could be that antibiotics are being prescribed in babies who are showing early signs of asthma and do not actually have a respiratory tract infection,' he said.