Wash your hands and you won't get a cold. You've probably heard that countless times.
Good hand hygiene is important for reducing transmission. But an increasing number of studies suggest that cold viruses primarily spread through the air we breathe.
Especially in certain types of rooms.
Ventilation plays an important role
"Even before the pandemic, it became clear that we had underestimated airborne transmission indoors for many years," says Jörn Klein.
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He is a professor at the University of South-Eastern Norway and an expert in infection control.
"Small virus-carrying droplets can remain airborne for a long time. In rooms with poor ventilation, large concentrations of virus can accumulate in the air," he says.
Klein stresses that catching a cold involves much more than simple 'hygiene.'
"It's largely a matter of indoor climate and ventilation," he says.
Large and small droplets in the air
Colds are often caused by rhinoviruses – small viruses that attack your body, leaving your throat sore and your nose runny.
Rhinovirus, our faithful winter companion.(Image: RCSB Protein Data Bank/CC0)
Rhinovirus exists in more than 150 different variants, which is why you can catch it over and over again – even though your immune system does its best to recognise is.
When people around you breathe, talk, cough, or sneeze, they release virus particles into the air.
These particles come in two forms:
Large droplets that quickly fall to the ground.
Small particles – aerosols – that can remain airborne for many minutes.
Many have feared droplet infection.
But several experimental studies in recent years have shown that it's primarily the small particles that spread the common cold.
Poorly ventilated rooms
Jörn Klein is a professor and expert in infection control.(Photo: University of South-Eastern Norway)
Even when an infected person is simply speaking or breathing normally, cold viruses can be released into the air through small droplets.
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These particles are so small that you can inhale them deep into your airways – and end up with a severe cold.
In controlled experiments, researchers have shown that simply breathing the same air as an infected person can be enough to catch a cold.
"Yes, the infection can be inhaled far beyond the classic one- to two-metre distance," says Klein.
So avoiding close contact alone is not sufficient.
If the room you are in has poor ventilation and stagnant air, the virus gets especially favourable conditions to spread.
This can happen on public transportation, in offices, or in classrooms. And of course at home, if you live with others. Especially if the air also has low humidity.
What about coughing and sneezing?
The large droplets expelled from the mouth and nose during coughing and sneezing can also transmit infection.
Simply breathing the same air as someone who is infected may be enough to catch a cold.(Stock photo: Gorm Kallestad / NTB)
But this mainly happens at close range – and only for a short period.
Because these larger particles fall to the ground quickly, researchers now believe they play a smaller role in transmission.
And what about hand hygiene?
Research confirms that you can also be infected with cold viruses by touching surfaces that others have touched – and then touching your nose or eyes.
"Infection via hands and surfaces still occurs," confirms Jörn Klein.
"But taken together, research suggests that this route of transmission probably plays a smaller role than we previously thought," he says.
Improve your indoor climate
For many years, we have thought of colds as a hygiene issue.
Much of the focus has been on handwashing.
Or we've assumed that coughing and sneezing, which send large amounts of virus-laden droplets into a room, have been the main route of transmission.
Many of us have also noticed that it's during the winter months – when we spend extra time indoors – that we most often catch colds.
Researchers now believe they understand more clearly why this happens.
"I believe that going forward we should think more broadly about preventing transmission," says the professor.
"Good ventilation, sufficient air exchange, and increased awareness of indoor climate should play a much bigger role. This is especially important in buildings where many people spend long periods together, such as schools, kindergartens, workplaces, and public transport," he says.
A simple air-quality monitor like this one, developed in Norway with support from the Research Council, measures carbon dioxide (CO2) levels indoors. According to one study, this can provide an indication of indoor ventilation and potential virus spread, for example in office spaces.(Photo: Airthings)
