"Bundle Up Or You'll Catch a Cold" and Why We Really Get Sick

5 years ago

Growing up, I was told that getting chilled outside would give me a cold. "Put on your coat or you'll get sick!" my mother would shriek as I blasted out the door.

It's true we're more likely to catch colds and flu during winter. But we don't catch colds or flu from going outside scantily clad.

Photo by Melissa & Bryan Ripka (Flickr).

If you read signs posted in schools and doctors' offices, you know that respiratory viruses are transmitted primarily by touch and by inhaling infected droplets. But how does that translate to more colds and flu in the winter? The answer does involve cold air, but has nothing to do with our bodies feeling chilled.

We Breathe in More Particles, More Deeply

Ongoing studies at Mount Sinai School of Medicine have turned up several explanations. The research relates to nasal and throat secretions laden with viruses. They disperse differently in cold air.

  • When a person spews out viruses by sneezing or coughing, the airborne droplets are much smaller at the lower temperatures and lower humidity of winter. Smaller droplets carry farther and stay suspended in the air longer, thereby increasing the likelihood they'll be inhaled by someone else.
  • These smaller droplets can be inhaled more deeply into the respiratory passages and lungs, increasing the chance that the person inhaling them will be infected by the virus.
  • In summer's warmer temperatures and higher humidity, airborne droplets are bigger and tend to sink to the ground quickly. At 75-80 degrees Fahrenheit, the risk of infection by droplets suspended in air is virtually zero.
  • Flu viruses are more stable in colder, drier conditions -- meaning that they remain infectious for a longer period after leaving the sick person's body.
  • Cold air makes the normal mucous in our respiratory tracts more viscous and sticky. The sticky mucus clogs up the movement of the tiny hair-like cilia that normally move in waves to expel particles from our respiratory passages. So inhaled viruses tend to stay where they land, reproducing and causing a respiratory infection.
How Do We Avoid Infection?

First of all, get a flu shot! Beyond that, avoid standing close to someone who's sneezing or coughing. The sooner you leave the area, the better. If you're the sick one, cover your nose and mouth with a sleeve when you sneeze or cough. Keep those virus-laden particles out of the air and off your hands.

Guard against transmission by touch as well -- viruses linger on doorknobs, ATMs, money, pens, phones and all kinds of other place, so when in public, wash your hands often and avoid touching your eyes, nose, or mouth.

More Resources

For more information about the flu, check out this CDC web page.

To see the Journal of Infectious Diseases article that reports these viral-transmission discoveries, click here.

To hear an NPR interview with Dr. Peter Palese of Mt. Sinai School of Medicine about his team's findings, click here.

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