Boys with asthma are twice as likely as girls to visit their primary doctor with worsening symptoms during the first weeks of the new school year, the BBC reports.
Being exposed to new viruses at school and a relaxed use of inhalers over the holidays could be factors, experts say.
In recent years, there has been a sharp rise in school-age children with asthma being admitted to hospital in September, around the start of the autumn term.
These increases, called the “back to school” effect, were also found in Scotland and Wales.
“Back to school asthma” is thought to account for up to a quarter of serious bouts of asthma in many northern hemisphere countries.