The common cold is likely the most easily recognized illness. Symptoms include a runny nose, sore throat, itchy eyes and low-grade fever. The illness is usually mild, lasting one to two weeks and requires nothing more than supportive care at home. However, while mild, it often results in days of lost work, lost productivity and lost income.

The common cold is the leading cause of doctor visits, and American school children miss about 22 million school days each year due to colds. Some estimates are that 1 billion colds occur each year in the U.S.¹ Children may have between six and 10 colds each year and the average adult suffers between two and four each year.

In the U.S. the majority of colds appear to occur during the fall and winter months. In the past, seasonal variations have been attributed to staying indoors during cold weather, lower vitamin D levels from lack of sunshine and close quarters with others who may be ill.

Growing up, your mom may have told you to stay warm and out of the cold to stay healthy. You may have dismissed this advice as an old wives’ tale, as colds are caused by viruses and not by the weather. However, recent research has demonstrated that while viruses trigger your symptoms, cold weather has a significant impact on whether you “catch” a cold.²

How a Cold Starts

A cold passes through direct physical contact with one of nearly 200 viruses that can trigger symptoms.³ Someone who has a cold can pass it to you by touching your hand, sneezing near your face, or through contact with their body where the cold virus has been sprayed after a cough or sneeze. You may also acquire the virus after touching a door handle, computer keyboard or utensil where the cold virus has been deposited, and then touching your face or nose.

Once inside, the virus attaches itself to the lining of your throat or nose, triggering your body’s immune system to send white blood cells. If you’ve built antibodies to this virus in the past, the fight doesn’t last long. However, if the virus is new, your body sends reinforcements to fight, inflaming your nose and throat. With so much of your body’s resources aimed at fighting the cold, you are left feeling tired and miserable.

Dr. William Schaffner, chair of the department of preventive medicine at Vanderbilt University School of Medicine, points out that you may not even know you’ve been around someone who has been sick, saying:⁴

“You can catch a cold even when you cannot recall being around anyone with a cold. It’s not really a mystery — people can excrete [exhale] the cold virus for at least 24 hours before they become sick. Thus, the person from whom we caught the cold was without any symptoms when [he] passed the virus on to us.”

You may have noticed that some people get more colds than others, or people you’re with get sick when you don’t. There are several factors that increase your potential risk for a cold, including:^5,6

Cold Weather Closely Associated With Your Immune Function

Cold weather not only drives people indoors where exposure to those who are already ill increases, but the temperature may also increase your overall risk. Although the name implies temperature has something to do with an increased risk, researchers from Yale University only recently discovered cold temperature weakens your first line of immune defense in your nose.⁸

Using a rodent model, scientists modified a strain of rhinovirus to enable it to infect mice in order to demonstrate the increased number of people with colds in the winter weather had a biological component as well as a behavioral one.

Researchers built their model based on the knowledge that rhinoviruses, responsible for nearly 50 percent of all colds, replicate faster at lower temperatures. They then asked if previous research wasn’t looking at the wrong side of the equation, and instead should attempt to determine if your ability to fight these growing invaders was at all compromised by temperature.

Led by immunobiologist Akiko Iwasaki, Ph.D., the team designed an experiment in which they were able to observe what happened to nasal cells when the rhinovirus attacked.⁹ When the tissue was exposed to rhinovirus at body temperature, the cells were able to effectively mobilize the immune system to kill the virus before the viral cells replicated. However, at lower temperatures, the cells managed only a weak defense that allowed the virus to replicate quickly and become established.

To test the theory that at colder temperatures the immune system responds slower than at body temperature, they analyzed the chain of proteins defending the cells and found when the genes responsible for making the proteins were shut off, the cells couldn’t mount a defense, even at body temperature. The rhinovirus may have found a niche by invading the body through the nose where the air is often cooler than body temperature.

The results of the study from Yale University were confirmed by researchers from Sweden and Scotland when they collected over 20,000 nasal swabs over three years and compared the results against local weather data,¹⁰ finding you are much more likely to get sick when it’s cold than during warmer weather.