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    It's no surprise so many people get colds and the flu mixed up. They're both contagious illnesses that affect your lungs and airways, and they have many of the same symptoms. But unlike a cold, the flu can cause serious and even life-threatening problems. That's why it's important to be able to tell them apart.

    With the flu, taking antiviral medications in the first 24 to 48 hours can make your symptoms less severe. "Sometimes that can make the difference between [being] sick for a week, or 2 weeks or longer," says Len Horovitz, MD, of Lenox Hill Hospital in New York City.

    Use these clues to help you decide what you have and what to do about it.

    The Flu

    It usually lasts 1 to 2 weeks and gets better as time goes on.

    You probably have it if:

    You feel miserable all of a sudden. "With the flu, you usually go from feeling fine to feeling like you were hit by a truck, often in less than an hour," Horovitz says.

    You have several severe symptoms. Though you may have cold-like issues such as the sniffles and stuffiness, the flu causes worse symptoms, too. Extreme exhaustion, headaches, feeling achy, a fever and chills, and skin that's sensitive to the touch are all signs.

    Your cough is "dry." That means it doesn't loosen mucus in your airways. This type of hacking can be painful.

    Colds

    These usually last 7 to 10 days and get better on their own.

    Chances are you have one if:

    You're sick but can still function. "Unless you have another medical problem, a cold doesn't usually cause the same extreme exhaustion that the flu does," says Aaron Clark, MD, at The Ohio State University Wexner Medical Center.

    You have slightly different symptoms every day or 2. For example, you might start with a stuffy nose, then get a sore throat, and have sinus or head pain before you feel better.

    "Cold viruses can cause some flu-like symptoms, but you usually have just a few at a time, rather than all of them at once," Horovitz says.