Employees who come to work even when they’re aren’t feeling well may end up costing companies more in lost productivity than their employers pay for sick days and other medical and disability benefits.

A new study shows that work slowdowns caused by illness on the job, known as “presenteeism,” may account for up to 60% of employer health costs. Researchers say the findings suggest that companies may need to take another look at their health care spending.

The study showed that for many conditions, the costs of presenteeism were far greater than other employer-related health care costs, such as absenteeism or health and disability benefits. For example, presenteeism due to headaches accounted for 89% of the total cost of productivity losses using average estimates and 49% using low estimates. For allergies, the costs of on-the-job productivity losses accounted for as much as 82% and as little as 55%.

The estimates were based on a database of about 375,000 employees, which included information on insurance claims for medical care and short-term disability over three years.