Your Mom Was Right: Cold Weather Really Will Make You Sick

Ever notice how everyone starts getting the flu right after the outside temperature plummets? A new study confirms what most people take as common sense: Once the days get really cold, we're much more vulnerable to the flu and other viruses.

Nicklas Sundell, a researcher with Sahlgrenska University Hospital, was the lead author on the study conducted by the University of Gothenburg in Sweden. It found that the flu season really begins after the temperature outside consistently drops below freezing and humidity gets low.

“According to our calculations, a cold week with an average temperature below zero degree Celsius precedes the start of the flu epidemic,” said Sundell.

"Cold and dry weather and small aerosol particles are important perquisites for the flu epidemic to take off. But cold weather isn't the only contributing factor," he continued. "The virus has to be present among the population and there have to be enough people susceptible to the infection."

The study covered three seasons and included 20,000 virus samples. Using weather data from the Swedish Meteorological and Hydrological Institute, the researchers matched temperature trends to the frequency of flu diagnoses.

The results were clear: Outbreaks of the flu were precipitated by the first cold chill of fall or winter.

You may have heard that it's a myth that the cold makes you sick; strictly speaking, that's true. Temperatures don't cause the cold or the flu, viruses do.

But it seems the drop in outdoor temperature makes it easy for infections to take off. The researchers point out that these findings support the theory that aerosol particles that contain viruses spread more easily when the weather is cold and dry. As the air gets colder and dryer, these particles become airborne more easily.

Nevertheless, the diseases can continue to spread even when the temperatures rise.

"Once the epidemic has started, it continues even if temperatures rise. Once people are sick and contagious, many more may become infected,” said Sundell. "Cold weather isn’t the only contributing factor. The virus has to be present among the population and there have to be enough people susceptible to the infection.”

The authors also note that the effect they found is not limited to the flu but applies to other viruses, such as the RS-virus and the coronavirus, that infect the respiratory tract.

Ironically, the researchers found that rhinovirus, the most common cause of generic "colds," are not precipitated by any weather conditions and are as likely to appear any time of year.

Is there any point to a study that confirms what people already know? Should we be surprised that the cold weather at the beginning of the flu season actually does, in part, cause the flu?

It is important for scientists to investigate claims that seem like common sense, because sometimes common sense is wrong. But these investigations can also lead to a better understanding of how flu develops in the population, which may lead to better treatments and preventive health measures.

“If you can predict the start of the annual epidemics of the flu and other respiratory viruses, you can use this knowledge to promote campaigns for the flu vaccine and prepare emergency wards and hospital staff in advance for an increased number of patients seeking care," said Sundell. "The recommendations are the same as previous years: vaccination of risk groups, cough and sneeze into your elbow, and remember to wash your hands."

Photo credit: Ryan Hyde