Doctors used to call influenza "knock-me-down" fever, and there was a reason for that. Anyone who's suffered through a bout of it knows the miseries: the headaches, the throat that feels scrubbed with sandpaper, the fever so high you're floating on the edge of delirium. And then there is the cough, the muscle pain, the general misery. Worse still: Flu can kill, though not often, and typically only the very young, the elderly and those with compromised immune systems.
So what do you do? Because fever-reducing medicines make you feel better, the natural thing is to reach for that bottle of ibuprofen or acetaminophen and power through. New research, however, suggests that may be exactly the wrong approach.
A recent study published in the Proceedings of the Royal Society by researchers at McMaster University found that reducing your fever is likely to extend your illness. Moreover, fever-reducing medicines can increase the rate of transmission by making you feel well enough to go back to work or school and cough and spread your germs. The fact that you feel better doesn't mean that you are better, just that you've become a more likely virus delivery vehicle.
Paul Andrews, an evolutionary biologist at McMaster and one of the coauthors of the Royal Society article, puts it this way: "I think it's pretty darn clear that fever is an evolved adaptation. Fever activates, regulates and promotes the immune system."
In warm-blooded organisms such as birds and mammals, Andrews explains, "our brain kicks in to regulate our body temperature." Cold-blooded reptiles and fish have their own strategies: "Fish move into warmer water to raise core body temperature when they have an infection." So fever is what evolutionary biologists call evolutionarily conserved: It's there for a purpose, and during acute illnesses, it can be good for the host. High temperatures may kill some germs, but even more important, fever sets in motion an entire immunological process.
The idea that reducing fever with medication might make you sicker is not new. Studies of rhinovirus (a cause of the common cold), chickenpox and malaria have suggested that lowering temperatures prolongs and worsens infections. According to evolutionary biologist Paul Ewald of the University of Louisville, it's not only the reduction in fever per se that's dangerous but the reduction in inflammation. That suggests that aspirin and ibuprofen, which curb inflammation as well as fever, might be worse to take when you have the flu than acetaminophen, which doesn't.
But acetaminophen is no answer. According to a 1989 study in the Journal of Pediatrics, children with chickenpox who took acetaminophen remained sick and infectious longer than those who didn't.
And what about taking that mixed cocktail of over-the-counter medication to stop the sneezing and coughing? Ewald says that although this might cut down on spreading infections, it's unlikely to help you get better faster. Sneezing and coughing help clear irritants from your respiratory system. Stopping sneezing and coughing might reduce transmission, but, as virologist Earl Brown of the University of Ottawa says, it also means you're not clearing out irritants. Sneezing and coughing gets virus out of your nose and lungs, so stopping that sneeze might keep you sicker longer.
And there's still another twist: Fever isn't always your friend. As Ewald argues, fevers and inflammation in chronic as opposed to acute infections might actually be harmful. If persistent infections keep causing inflammation and damaging cells, the harm done to the body could be significant. You want to cut down on persistent inflammation, which is why anti-inflammatory drugs are used in arthritis and other inflammatory conditions. Long-term inflammation, Ewald says, can cause cancer and other harmful effects.
Untangling these runic complications will take much more research. But what we can say unequivocally is that there's likely to be a real evolutionary benefit to staying at home while you're acutely sick. Andrews points out that taking fever reducers may push circulating influenza toward virulence by allowing nastier strains to spread. Ewald makes the same point in reverse: One way to push influenza strains toward mildness is to keep everyone sick enough to medicate at home instead. If you had a case of flu so mild you barely noticed it, you'd only spread mild germs. So, logically, if the really sick didn't go out, the influenza strains that managed to spread would likely evolve toward mildness. That's good for everyone.
The long and short of it: If you're sick enough to need medicine, do yourself and everyone else a favor. Just stay home.
Wendy Orent is the author of "Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease" and the new e-book, "Ticked: The Battle Over Lyme Disease in the South."