When is your cold most contagious?

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If you get to the office and notice your throat is a bit sore, it may be time to head home.

“When you are infected with a cold, you’ll be most contagious about a day before you show symptoms,” said Dr. Jane Heffernan, a professor at York University’s Faculty of Science who specializes in infectious diseases.

“[You’re still contagious] five to seven days after you show symptoms.”
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In other words, you’re most likely to pass on the virus around the same time you realize you’re getting sick, and just shortly after.

While many people assume you need to have obvious signs of a cold, like a runny nose or cough to pass it on, it may come as a surprise that the virus is transmittable before your symptoms begin.

“If you have friends or family members that have a cold, then you’ve probably been exposed to it,” Heffernan explained. “The best thing to do is to make sure you are practicing proper hand washing.”

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How colds spread

According to the Canadian Centre for Occupational Health and Safety (CCOHS), there are more than 200 viruses that can cause colds, but the main family of viruses are the rhinoviruses. These viruses can live on surfaces for hours after contamination, Heffernan said.

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When you’re infected with a cold (even when you aren’t showing symptoms), respiratory droplets that contain the virus spread through mucus membranes, which include our eyes, nose and mouth, said Jessica Mudry, an assistant professor of professional communication at Toronto’s Ryerson University and an expert in public health messaging. “Those are the three entry points or gateways.”

Mudry said that when you have a cold, you are likely touching your nose or mouth often to deal with the discomfort and obvious symptoms like a cough or runny nose. When you do this, the virus ends up on your hands, which is how it lands on things you touch like a door handle or keyboard, for example.

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“If I have a cold and I wash my hands, I probably don’t have the virus on my hands. But if I then touch my nose and go and shake someone’s hand, I’ve just taken some of the virus out of my nose… and put it on someone else’s… body,” she explained.

“If that person goes and washes their hand, chances are they won’t get a cold. But if they take that hand… and then touch one of their mucus membranes, there’s a possibility that the virus can then take up residence.”

Your cold is likely less contagious near the end of its life, clocking in around day seven or eight, depending on the severity of your illness. “The [virus] ramps up, comes to a peak, then ramps back down,” Heffernan said.
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How to prevent passing on a cold — or catching one

Like Mudry pointed out, it’s easy to pass on a cold.

The CCOHS states since colds are highly contagious, they’re one of the leading reasons why people miss work each year. The centre estimates that adults suffer two to five colds annually.

One simple way to stop spreading germs? Keep your hands clean.

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“Washing your hands is so important because we tend to touch our eyes, our nose and our mouth, and if we have some of the virus on our hands, [it can be transmitted],” Mudry said.
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Heffernan echoes this, and added that practicing safe social distance from other people helps prevent passing on the virus, too. This means minimizing close contact with people who have a cold, and avoiding skin-to-skin touching.

But, if you practice hand washing and social distance, you shouldn’t be too concerned with passing on or catching a cold.

“The thing is, a lot of people have natural behaviours and don’t necessarily adopt the practices that may be optimal,” Mudry said.

So if you’re really sick, it’s best to take the day off and stay indoors. That way, you’re giving your body time to fight the virus, and reducing the chance you’ll give it to someone else.