Here’s How to Tell if You Have a Cold or the Flu

Your nose is dripping like a leaky faucet, your throat is sore and you can’t stop sneezing. You don’t have a fever, but you feel wiped out—like you could curl up on the floor and fall asleep. Do you have a cold or the flu?

If you guessed cold, you’re probably right. But experts say that differentiating the common cold (an upper respiratory infection) from the flu (influenza) can be trickier than most people assume.

“There is huge overlap among non-influenza viruses and the symptoms produced by influenza and other bugs,” says Dr. Bruce Barrett, a professor of family medicine and community health at the University of Wisconsin. While many people associate the flu with a fever, Barrett says this isn’t always true. “Unless someone comes in during the peak of flu season”—a two-month period that typically lands somewhere between November and March—“I can’t tell very well whether it’s cold or flu based solely on symptoms,” he says.

But while colds and flu can in many cases look a lot alike, there are some predictable differences. For one thing, colds usually take a few days to build up, while the flu comes on more abruptly. “Sometimes [a flu] patient goes from well to very sick in a few minutes,” says Dr. Jeffrey Steinbauer, a professor of family and community medicine at Baylor College of Medicine.

Cold and flu symptoms

A cold typically lasts about three to five days, while a flu tends to linger about twice that long, Steinbauer says. Also, a fever is much more common among flu patients, and the same is true of headaches, body aches and a dry cough. On the other hand, if you have a cough that produces a lot of fluid or mucous, you have a sore throat and you’re sneezing or dealing with a runny nose or head congestion, all of those symptoms are more typical of colds, he says. (Worth noting: a stomachache, diarrhea, and other GI symptoms can crop up in kids, but they’re not common among adults suffering from either a cold or flu. If you have these symptoms, you’re probably dealing with a stomach virus or a food-borne illness.)

The timing of your symptoms can also be revealing. Colds are most common in early fall (usually right when students return to school) and in spring. But they’re a year-round concern, says Dr. William Norcross, a principal investigator in public health at the University of California, San Diego. “They are somewhat more common in winter when people commonly gather indoors,” he says. But you can catch a cold any time, whereas the flu is usually confined to its winter schedule.

Look at the two under a microscope, and you’ll see more differences. The flu is spread by two families of virus known as influenza A and influenza B, Norcross explains. Within these two families there’s a great deal of variation, which is why the composition of the flu vaccine changes from year to year and is not always as effective as public health officials hope.

Common colds, on the other hand, are caused by more than 200 different subtypes of respiratory virus, says Dr. Kyle Sue, a clinical assistant professor of family medicine at Memorial University of Newfoundland in Canada. These include rhinovirus, coronavirus, adenovirus, respiratory syncytial virus (RSV) and others—each of which can result in different symptoms and severities.

While the common cold and flu can seem quite alike, there’s one very important distinction: one is deadly, and the other is not. “Influenza kills about 35,000 Americans per year, whereas colds rarely cause lasting harm,” Norcross says. For the most vulnerable people—which includes those with weakened immune systems, the very old and babies born prematurely—the flu is a common cause of pneumonia and death, the CDC warns.

How to prevent spreading the flu

Because of these risks, and because the symptoms of colds and flu can be hard to tell apart, experts say that it’s vital for people to take steps to prevent the spread of these viruses. “When you are sick with influenza or a cold, your mucus, saliva and everything coming from your nose, mouth and throat down to your lungs is teeming with millions of highly infectious virus particles,” Norcross says. Sneezing, coughing or any other activities that transfer your mucous to your environment could make other people sick.

If you’re feeling unwell, the best thing you can do is to isolate yourself until your symptoms go away. “If you go to work, the store or take the subway, you are likely to spread the illness,” he says. If you have to leave the house, avoid touching your mouth or nose, wash your hands frequently and try to cough or sneeze into the crook of your arm.

It’s also crucial that you get a flu shot—preferably before the end of October. Depending on how well the vaccine’s developers did at anticipating the season’s influenza strains, the flu shot’s effectiveness can vary from about 50% to 90%, Norcross says.

While saving yourself from suffering is one good reason to get the shot, another is to save lives. By vaccinating yourself against the flu, you’ll be much less likely to acquire and spread it to at-risk groups, Barrett says. “If we can get 30% to 40% of the population vaccinated, we’ll save 10,000 lives,” he adds.

How to treat the flu

When it comes to treating the flu, antiviral drugs (such as Tamiflu) can reduce the illness’s length and severity, Barrett says. But these drugs need to be taken right away—within 36 hours once symptoms begin. “They’re useless after that,” he says. If flu symptoms hit you hard and you can see a doctor right away, these drugs may be helpful. Also, anyone at risk for serious complications—the very old, the very young and those with weakened immune systems—should tell their doctor if they’re experiencing symptoms.

But for healthy adults and kids, colds and flu usually don’t require a doctor’s attention. “I do not want people coming in for upper respiratory infections, because there’s not much we can do for them,” Barrett says. Even for people who believe they have the flu, most are better off just weathering the illness at home, he says. You’ll be less likely to infect others that way, he says, and both colds and flu resolve on their own—usually within a week. If that much time passes and your symptoms aren’t improving, or they seem to be getting worse even after the first few days, it’s time to see a doctor. The same holds if your fever reaches 103 F.

If your symptoms are making you miserable, over-the-counter medications can offer short-term relief, says Steinbauer. You could take aspirin or acetaminophen for a fever, or decongestants for your runny nose. Zinc lozenges may also help curtail your cold, research has found. But time, rest and plenty of water and other fluids are the only true cures.