By Lead writer: Amanda Gardner
February 29, 2016

Think antibiotics are a quick fix for a stuffy nose, cough, and sore throat? You're not alone. Tom Campbell, MD, a family physician from Rochester, N.Y., says that patients often plead for antibiotics for garden-variety cold symptoms, saying everything from "The last time it helped me completely" to "I have to go to my daughter's wedding" and "There's this terrible green guck coming out of my nose."

There's just one problem. While antibiotics are excellent at killing bacteria (as long as you match the right drug to the right germ), they're useless at killing viruses. And viruses, including the flu, cause 90% of respiratory infections. "Most upper respiratory infections are caused by viruses; a minority are caused by bacteria," says Lauri Hicks, MD, medical director of the Centers for Disease Control and Prevention's "Get Smart: Know When Antibiotics Work" program. For example, Dr. Hicks notes, only 2% of sinus infections are caused by bacteria and require an antibiotic.

So what, you say? Antibiotics might help and they certainly can't hurt, right? Wrong. The evidence is piling up that using antibiotics indiscriminately is dangerous from a public health standpoint (it can breed drug-resistant bacteria) and even personally (they kill off healthy bacteria in your body and may let toxic germs gain a foothold).

However, there are times when the icky green goo in your nose or the hideous rattling cough in your chest might benefit from the antibiotic superhero treatment. So how do you know if you need one?

Doctors consider some guidelines when mulling this question, although it's still a gray area. "It's an inexact science," says Frank Esper, MD, a pediatric infectious diseases expert at Rainbow Babies & Children's Hospital, in Cleveland. Its difficult to distinguish a severe viral infection from a mild-to-moderate bacterial infection based on symptoms alone.

So physicians often use their spider senses—a combination of experience and science—when deciding to dole out an antibiotic. Here are five things most doctors take into consideration when making that decision. (View this list as a slideshow..)

  • Fever. If you have fever, shakes, and chills, you could have a bacterial infection, but those are also common with a viral illness such as the flu, Dr. Esper says. Physicians will weigh your likelihood of having the flu—Is it circulating in your area at the moment? How many patients has he or she seen with the flu that day?—against the possibility of a bacterial infection. If you have a fever, and flu is circulating in your community, you'll probably leave the doctor's office without an antibiotic. Next year, get a flu shot.
  • Length of time you've been sick. Viral infections that hang around for a while can sometimes morph into a bigger problem, such as a sinus infection, and bacteria may join the party. So if your symptoms have been lingering for weeks, your likelihood of getting an antibiotic goes up. However, most of the time, long-standing symptoms are due to a virus, not bacteria, says Dr. Campbell. Final verdict? Its still not the best way to determine your need for antibiotics.
  • The color of your goo. Nasal secretions tend to be thin and clear during a viral infection, while green or yellow mucus can be a sign of bacteria. This one is tricky, though; most greenish discharges are viral. Overall, mucous color is considered an unreliable indicator of the need for an antibiotic.
  • Your sore throat. Although it's red and looks terrible to you, your doctor may also look for white spots, which can be signs of bacteria, before considering an antibiotic. Most colds start with a sore throat, but a sore throat without other cold symptoms (such as a runny nose) can be strep throat, which does require antibiotics to halt the dangerous bacteria. To know for sure, you need a culture or rapid antigen test, which takes less than 20 minutes and can be done while you wait.
  • Testing. A lab test is the only ironclad way to determine if you truly need an antibiotic. A physician can collect a sample of bodily gunk (whatever you can cough up or blow out of your nose), or take a throat swab. In general, a culture, in which bacteria are grown in the lab and tested, can take a day or two. Doctors often forgo the expense and time of a lab test if they think they can make a best-guess decision based on the above symptoms.