Recent hot weather increased employee absences in a third of small and medium enterprises (SMEs).
At least 30% of businesses saw more staff call in sick since the start of the summer, according to a study commissioned by PMI Health Group.
But 54% of managers and owners questioned said they do not operate flexible working policies that allow staff to take time off at short notice.
PMI Health Group director Mike Blake said: “It is perhaps unsurprising to find the recent heatwave has had an effect on absence, but the survey results highlight the need for businesses to understand whether this is caused by illness or lifestyle.
“Flexible shift patterns will allow employees to fulfil their required hours without feeling their work-life balance is compromised.”
Blake added that companies could encourage staff to lead healthier lives, putting schemes in place to help them do so.
The study found that 71% of SMEs find it easier to engage employees in wellbeing schemes during the summer months.