When Am I Contagious?

When Are You Contagious With a Cold?

Group of people wearing protective masks.
Nobody wants your germs. Ghislain & Marie David de Lossy/Cultura/Getty Images

The term contagious means able to spread from one living organism to another. In this case, we're referring to people. When you are sick, you are considered contagious when you are able to spread your illness to someone else. Although we don't know the exact amount of time each person will be contagious when they are sick, there are general timelines for most illnesses. 

How Long Am I Contagious With a Cold?

Colds are highly contagious. They are caused by over 200 different viruses and are the most common illness in the world. If you get one, you are most contagious 2 to 4 days after your symptoms start. But you can actually spread the virus for up to 3 weeks!

When Are You Contagious With the Flu?

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Influenza, the actual flu (which is a respiratory illness - not vomiting and diarrhea), is another highly contagious virus. One reason is spreads so easily is because you are actually contagious before your symptoms start. 

Influenza can be spread from one day before symptoms appear to 7 days after they start. 

Your best defense against the flu? Get your flu shot. And wash your hands - correctly. Every time. 

When Are You Contagious With the Stomach Flu?

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The stomach flu is not really the flu at all. It is a gastrointestinal (GI) bug typically caused by one of a few different viruses. The most common cause of "stomach flu" is norovirus. This very contagious virus can be spread a day before your symptoms start. It is most likely to spread to others when you are having symptoms and the first three days after they stop but it's actually possible to spread it for three weeks after you get better. Yikes!

Is Bronchitis Contagious?

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Because bronchitis is caused by a number of different viruses, whether or not it's contagious isn't always an easy question to answer. Most viruses that cause bronchitis are contagious, but that doesn't mean they will lead to bronchitis in someone else. 

Bronchitis is swelling in the airways but a virus that causes this swelling in one person won't necessarily do the same thing to another person. The same virus could cause different respiratory symptoms in someone else. So even though you are contagious when you have bronchitis and can make other people sick, they may not develop the same symptoms you have. 

A more in depth explanation can be found here:

Is Pneumonia Contagious?

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Even less straightforward than bronchitis, is whether or not pneumonia is contagious. Most types of pneumonia are not contagious in the typical sense of the word. Meaning you won't get pneumonia just from being around someone with pneumonia. But that isn't true of all types and it doesn't mean you won't get sick at all either. 

Many times, pneumonia develops after a person has the flu or another respiratory illness. So you may have pneumonia but you could still give someone else the flu. 

The one real exception is Mycoplasma pneumonia (also known as walking pneumonia). This typically mild illness is contagious and can be passed from person to person. 


Another important tip to keep in mind - stay away from people who are at high risk when you are sick. Although no one in your office or school wants your germs either, those who are elderly, babies and people with compromised immune systems are more likely to get seriously ill if you expose them to your illness. 

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