As temperatures drop and influenza season ramps up, one thing seems certain: Going outside with wet hair is like playing Russian roulette with the cold and flu gods.
On the surface, the connection between wet hair and the sniffles seems to make sense. It causes you to feel extra cold, making you vulnerable to viruses and bacteria lurking in the air.
But like many things in life, the truth is much more complicated.
Pass the hand sanitizer
Perhaps you've already come down with your first cold of the season. Or stood in line to get your flu shot. This, after all, is the start of the prime season for respiratory infections.
But do colder temperatures actually cause us to get sick?
The overwhelming consensus is no. Whether a person comes down with a cold or flu depends on exposure to the virus.
The idea that wet hair will make a person sick "makes no sense to me at all," said Dr. Heather Jenkins, a family physician in Vancouver. "I don't know where it comes from."
So wet hair or not, your chances of getting sick depend on whether you encounter one of the many respiratory viruses that circulate at this time of year.
If winter doesn't make us sick, why is this cold and flu season?
This is one of the big mysteries that's puzzled scientists for decades.
Influenza is spread primarily through droplets that are airborne when an infected person sneezes, coughs or even talks. It's less common for the flu to be spread by touching an infected surface, such as a doorknob, for instance.
Many experts say that influenza season occurs during the winter months because people are more likely to be indoors, allowing for easier transmission of the virus. But plenty of people are in confined spaces all year round – and yet we see little flu activity in the summer.
In 2007, however, researchers published a study in the journal PLOS Pathogens that offered a different explanation. Using guinea pigs, the researchers discovered that the flu virus spread quickly and easily at low temperatures, around 5 C, and hardly at all when temperatures rose to 30 degrees. Low humidity was also linked to increased flu transmission.
The study authors say the flu virus survives best in cold, dry air, which explains why we see so much of it during winter.
The same could be true for cold viruses, according to the U.S. National Institute of Allergy and Infectious Diseases.
Some experts say more research needs to be done to fully understand how seasonal changes and lifestyle, such as diminished daylight hours and back-to-school season, impact cold and flu season.
Maybe the old wives were right?
There is an important caveat to note. While gallivanting around town with wet hair won't cause a healthy person to get a nasty cold, it might make an individual an easier target for cold and flu viruses.
Britain's Common Cold Centre based at Cardiff University published a study in 2005 that found that people who had their feet chilled in cold water for 20 minutes were more likely to get a cold in the days that followed than a control group.
The researchers hypothesize that plunging the body's surface temperature causes blood vessels in the nose to constrict, allowing an already-present cold virus to flourish and turn into a full-blown sickness.
However, the science on the topic remains unclear.
So you don't have to develop a deeper relationship with your hairdryer this winter. But you should become a diligent hand-washer and get your flu shot.