Flu season has hit hard this year. Many people already down with the bug and feeling lousy are reaching for pain- and fever-reducing medications like ibuprofen and acetaminophen for a little relief.

While these medications can be life-savers in some situations, they may have a very unexpected consequence when it comes to the flu: They can actually increase its spread.

Using fever-reducing medications could increase the number of cases each season by as much as 5%. And this amounts to another 1,000 deaths from the flu each year.

It is not just that medicating ourselves (or our kids) allows us to be out in public more. There’s another reason that these medications boost the spread of the flu: Fevers help reduce the amount of virus in our bodies.

When fever-reducing medications are taken, the virus is likely to present in higher quantities, a new study has found. This phenomenon isn’t news, but seeing it played out on the entire population is.

“Because fever can actually help lower the amount of virus in a sick person's body,” lead author David Earn said in a statement, “and reduce the chance of transmitting disease to others, taking drugs that reduce fever can increase transmission. We've discovered that this increase has significant effects when we scale up to the level of the whole population.”

Using computer models to predict how much the medications might affect the spread of the flu in both human and ferrets (ferrets make excellent, human-like models for the flu), the researchers found that using fever-reducing medications could increase the number of cases each season by as much as 5%. And this amounts to another 1,000 deaths from the flu each year.

“People often take — or give their kids — fever-reducing drugs so they can go to work or school,” said Earn. “They may think the risk of infecting others is lower because the fever is lower. In fact, the opposite may be true: the ill people may give off more virus because fever has been reduced.”

So, except in the case of extremely high and long-lasting fevers, we should be a little less concerned with reducing fever and more aware of the purpose it serves, particularly when it comes to viral infections like the flu.

The results clearly suggest that we shouldn’t let fever-reducing medications be used as green-lights to go back to work or school before we’re really healthy.

“As always, Mother Nature knows best,” said David Price, the chair of family medicine at McMaster's Michael G. DeGroote School of Medicine, where the study took place. “Fever is a defence mechanism to protect ourselves and others. Fever-reducing medication should only be taken to take the edge off the discomfort, not to allow people to go out into the community when they should still stay home.”

Most treatment guidelines and medical textbooks say it’s safe to use medication to fight a fever. But, given the results of the new study, this approach may need to be reevaluated. If fever is very high, it may be necessary to take medication, but for mild ones, it's best to let the fever run its course, since that's proof the body is doing its job.

The study is published in the Proceedings of the Royal Society B.