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Why are colds more common in winter even though being cold doesn’t cause them? How can a doorknob or touching your eyes give you a cold and why do people get them after long-haul flights? There are many surprising facts about the common cold.

Cold weather isn’t the cause of colds

But we all know we’re more likely to suffer from them during the winter, so what’s the connection? Well I’m not sure it’s still fully understood, but there are a couple of good theories. 

The first is that droplets of infected mucus expelled from someone when they sneeze or cough, travel faster when the air is drier.  This is because the droplets dry out, becoming smaller and lighter and so fly through the air more easily. The theory goes that in cold weather the air is less humid, the droplets travel further and are more likely to be breathed in by some other unfortunate person. 

The other effect of dry air is that it dehydrates the normally moist mucous membrane lining the nose. This is part of our defence mechanisms – inhaled virus particles are trapped in the moist lining and washed away by nasal secretions. 

Warm noses protect best

The second theory is all to do with the cold nose we experience in cold weather.  The first line of defence against viruses we breathe in is the rich blood supply in the lining of our nostrils and respiratory passages.  Immune cells in the lining are able to catch and hold the virus particles which are then washed out with nasal secretions.  

But when the nose is cold the blood vessels shrink to retain heat, and are not so efficient at catching the viruses.

Hence some viruses are able to gain entry to cells in the respiratory passages, and cause an infection.

The connection between long-haul flights and colds

Winter isn’t the only time we’re exposed to dry air – air-conditioning in hotels and offices, and in airplane cabins, has also been blamed for causing colds.  This is probably by the same mechanism as in winter – the dry air dehydrates the nasal lining which is then less effective at trapping inhaled virus particles.

Also, with a large number of people confined to a small space for long periods of time, it is inevitable that infections will be passed on, especially when they are as easily transmitted as cold and flu viruses.   

In addition travellers on long-haul flights are often deprived of sleep which lowers immunity, allowing infections to flourish.

The cold virus travels further than you think

When someone with a cold sneezes or coughs they expel mucus droplets containing virus particles, which are able to infect another person if breathed in or touched

Studies have shown that expelled droplets can travel as far as six feet!  This is partly due to the speed with which they travel – as much as 4.5 meters or 15 feet per second

Most experts agree that the most infectious time is when symptoms are at their height, so the lesson from this is not to get too close to someone with a cold and be sure to quickly turn your head the other way if they sneeze or cough.

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