How Long Are You Contagious With The Flu?

It's shaping up to be one of the worst flu seasons in years.

If you are one of the thousands of Americans who are sick with the flu, this one's for you.

You've spent the past couple of days cooped up in your house watching bad TV, fighting the fever sweats and expelling a baffling amount of mucus. As you start to resemble a human being again, you might feel pressure to head back to work.

But when is it really OK to return? Many people go back as soon as their symptoms start to resolve, which could be putting your co-workers at risk.

Those unpleasant symptoms are actually the result of your immune response battling the flu virus. Take fever for example. Your body starts a fever because the flu virus doesn't grow as well at high temperatures, and some immune cells actually work better.

All that gooey mucus you've been coughing up is good at trapping viruses before they can infect other cells.Your body is in an all out war, you against the virus. Immune cells seek out and destroy virus-infected cells.

As your airways get irritated, you cough and sneeze. And that's exactly what the flu wants. That's because the flu is spread from person to person in virus-containing droplets that are produced when a sick person coughs, sneezes or even breathes. When you cough, tiny droplets that fly from your mouth can travel as far as 20 feet at speeds ranging from 25-50 mph. Sometimes they can stay suspended for hours.

If someone inhales those particles, they can become infected. The flu can even be transmitted if someone touches a surface contaminated with flu and then touches her face or mouth. That's why hand-washing is so important when you're sick. But the best way to prevent spreading the flu is to stay home if you can.

So how long are you really contagious with the flu?

The CDC says you are contagious one day before you start feeling sick and up to seven days after. If you're a kid, elderly, or have a weak immune system, you can be contagious for even longer.

NPR's Skunk Bear gives us an inside glimpse into how your body fights the flu, and when it's a good idea to head back to work.

Madeline Sofia, Meredith Rizzo, Adam Cole and Ryan Kellman produced this video for NPR. Daniela Sherer created original animations for the video.

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