Occupational health provider Arbo Unie expects a sharp rise in sick-leave reports among employees starting from September, which it has dubbed an official start of the “absence season,” as more and more people fall sick as the weather gets colder.

Based on analysis of sick leave reports from the years 2020 to 2025, Arbo Unie found that sick reports in September are on average 69 percent higher than in August.

“The post-summer rise does not mean workers suddenly have no desire to return to the job,” said an occupational physician from Arbo Unie Corné Roelen. “From September, many organizations get busier again, and people have more contact with one another. At the same time, the period when colds and flu play a larger role begins. That combination can explain why sick reports climb so clearly after summer.”

Nearly three-quarters of the days taken off in September last year were less than a week, while a typical absence period lasts about four days, Arbo Unie said. However, a “relatively larger share” develops into long-term absences. When it comes to those prolonged absences, mental health issues, including stress, are the leading cause.

Overall, absences are the highest in the winter months of January, February, and March, also driven in part by colds and the flu.