Feeling ill but convinced your co-workers will be lost without you? Forget about trying to be a hero. Instead, stay home and your boss will thank you for it later.

According to a recent Cornell University study, workers who come in sick cost their employers an average of $255 each year. That’s because sick workers work more slowly and have to repeat tasks, have difficulty concentrating and generally bog down productivity. They also tend to get their co-workers sick, a potentially larger problem that was not included in the study, which was published in the April issue of the Journal of Occupational and Environmental Medicine.

Economists even have a name for showing up to work when your health says you shouldn’t. It’s called “presenteeism.” Other studies have suggested that presenteeism costs U.S. businesses $180 billion annually in lost productivity. Hypertension, or high blood pressure, is the most costly ailment, costing employers more than $392 per employee annually. Allergies cost $271 and migraine headaches nearly $214 in lost productivity.

Further the study found that 61 percent of medical and lost productivity costs related to 10 common ailments, including colds, asthma and arthritis, were attributable to ill workers staying on the job.

The research does not mean that employees should stay home sick with every sniffle, but rather that employers have yet to realize the full financial impact of having sick employees show up for work, said Ron Goetzel, director of Cornell’s Institute for Health and Productivity Studies.

Despite the new research, employee absenteeism, the effects of which have long been documented, costs more. Absenteeism costs an average of $645 per employee per year, according to CCH Inc., a trade group that does an annual survey on the issue. The costs are higher due to the need to pay overtime or hire temporary workers to make up for those who are out sick.

Rather than coughing on your co-workers and starting an epidemic or repeatedly reading the same memo because you are in a fog due to a migraine headache, stay home and get well. It’s better for the bottom line and for you.