We've all heard warnings like this: "Shut the window! It's draughty in here and we'll all catch a cold!"
To take the wind out of draughts' sails, so to speak, let it be said at the outset that draughts themselves don't make you ill, such as viruses do. On the other hand, our bodies aren't entirely unaffected by a draught in a room. It makes things happen on and under our skin that can lead to a runny nose or stiff neck.
To understand the effect of draughts, you need to be familiar with wind chill, also known as the wind chill factor. It's the apparent temperature felt on exposed skin, a combination of the actual air temperature and wind speed. The higher the wind speed, the lower the apparent temperature.
"If it's minus 5 degrees Celsius and you're standing somewhere outside in calm air, your body heats a thin layer of air next to your skin," explains ENT physician Dr Thomas Deitmer, general secretary of the German Society of Oto-Rhino-Laryngology, Head and Neck Surgery (DGHNO-KHC). Like a wet suit in cold water, it insulates you from the cold.
But a cold wind blowing across your body continually carries this warmth away. The harder it blows, the faster your body loses heat and you feel cold. This effect is intensified if your skin is wet - for instance with sweat - because moving air evaporates the moisture faster, and thereby drains heat from your body faster, than calm air does.
When your body's surface chills in cold air, such as a draught, nearby blood vessels constrict, decreasing blood flow to minimize heat loss from the warm blood. This affects the mucous membranes in your nose and throat as well. A draught can also cause them to dry out, weakening their immune defence and making you more susceptible to cold viruses, points out Deitmer.
If you're healthy, you won't become ill simply by being exposed to a draught, though. But to be on the safe side, you could wrap a scarf around your neck or put on a cap when you ventilate a room.
Dr Michael Deeg, a member of the German Professional Association of Otolaryngologists (BVHNO), mentions another possible consequence of draughts: a stiff neck, particularly in warm weather.
"If you feel hot and sit in front of a fan or in the draught of an air-conditioning system, or roll down the window while travelling in a car, the air that blows over your warm and often sweaty skin can lead to neck tension," he says.
The body always tries to adapt its temperature to environmental conditions. "There are receptors on the surface of our skin that measure skin temperature," Deeg explains. "The problem with a slight draught is that the difference in temperature is also slight and not sufficiently detected by the thermoreceptors."
So the skin cools but the body doesn't react enough. This can cause the blood vessels in your neck to constrict and the muscles underneath to tense up.
What can you do to prevent draughts from getting under your skin, as it were? Operate fans in warm weather for short periods only, and make sure they're not too close to you. To keep yourself from becoming chilled by water evaporating on your skin after a swim, remove wet swimwear promptly.
Tempting though it may be to completely roll down the windows of a moving car when you're sweaty, don't. And don't let the air conditioning or ventilation directly blow on you.
In cold weather, experts say, there's no reason not to practice impact ventilation - ie opening windows wide for several minutes to allow fresh air into a room and stale air to flow out - if you have a healthy immune system. To reduce or prevent wind chill, you could briefly put on another layer of warm clothing or simply leave the room.