Here's the best way to figure out if you have a cold, the flu, or allergies

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Sniffle, sniffle.

When you wake up sick, with a scratchy throat, a stuffy nose, and a vague constellation of other miserable symptoms, it's important to figure out exactly what is ailing you.

Is it just hay fever, or are you contagious? Should you suffer through the work day with your cold, or are you about to unleash a nasty strain of flu on your whole office? How can you tell the difference?

We sorted through the research and talked to Dr. Robert Wergin, board chair of the American Academy of Family Physicians, who has seen plenty of sneezing, coughing patients since he began practicing medicine more than thirty years ago.

A three-step plan

There are a few key steps to help determine the difference between common causes of respiratory distress like the cold, the flu, and seasonal allergies. 

1. Think about the time of year.

In the fall, three-fourths of all circulating viruses are rhinoviruses, the most common cause of colds.

In the spring and summer, when colds still crop up but respiratory illnesses are less widespread, seasonal allergies run wild. (If you get allergies regularly, pay attention to which month they seem to strike each year.)

From late fall all the way through winter, meanwhile, you should be on the lookout for the flu, or influenza. Flu season typically peaks in February, though it can also do so as early as November or (as with this year) as late as the end of March.

2. Take stock of your symptoms.

A flu is, in general, more severe than a cold, and it is usually accompanied by a fever (over 100 degrees Fahrenheit), an achy body, and what the National Institutes of Health call "extreme exhaustion."

With a flu, "symptoms such as fever, body aches, extreme tiredness, and dry cough are more common and intense," the Centers for Disease Control and Prevention explain. A flu can also cause serious complications like pneumonia.

People with colds, meanwhile, are more likely to experience stuffy or runny noses.

Seasonal allergies, Wergin says, often come with itchy eyes, an itchy nose, and, subsequently, sneezing - though sufferers can also develop a sore throat from a post-nasal drip.

3. Wait and see - the duration of your illness matters.

This won't help you right away, but it's one thing doctors pay attention to when they're trying to figure out what's wrong.

You should get over a cold in three to seven days, though symptoms can linger for another week or so. A bad flu can sometimes last a little longer than a cold, with symptoms like fatigue persisting up to three weeks. And your allergies will stick around as long as whatever allergen triggers them is still in the air, which can be more than a month. 

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Whether you have a cold or the flu, try not to pass it on.

What to do next

"If you have standard symptoms and you're managing OK at home," then getting plenty of rest and fluids and using over-the-counter medications as needed is probably fine, Wergin says.

But if you think you might have a cold or the flu, try to avoid giving whatever you have to other people.

"If it goes beyond five to seven days, you ought to be checked by a doctor," Wergin adds. And people who are pregnant or have chronic health conditions should check in with their doctor sooner.

With some cases of respiratory discomfort, it's hard to tell exactly what's going on without conducting a test. The CDC says definitively figuring out the difference between a cold and a flu "based on symptoms alone" can be "difficult (or even impossible)." A team of Australian researchers conceded the same point, noting that "many viruses are known to cause clinical illness that is difficult to distinguish from influenza." There are plenty of clues that can help you figure out what's wrong, but you're often left without a perfect diagnosis.

While there's limited, uneven evidence that antiviral medications can help fight a flu if you get to your doctor early, "the best treatment of influenza is not to get it," Wergin says. "Get a flu shot."

A previous version of this story appeared in December 2014.