People are being made aware of the risks of leaving on a seemingly harmless setting in their cars for a long period of time. Forgetting to turn it off could lead to a sense of "uncontrollable tiredness" while driving, which can quickly become dangerous.
Many cars come with an air recirculation button, which prevents outside air from entering and keeps the air inside the car circulating. It can be helpful to cool off quickly during the summer, save fuel, and keep out pollution and bad smells when you're stuck in traffic.
However, as previously reported by the Daily Mirror, leaving the setting on for 20-30 minutes can be dangerous, as it reduces oxygen and increases carbon dioxide (CO2) levels, which can trigger drowsiness and reduce concentration. This was the case for Capital Breakfast and ITV's This Morning presenter Sian Welby, who learned about the risks first-hand.
The 39-year-old said at the time that it was only during a chance scroll on TikTok that she realised the car button was part of a problem she had regularly been experiencing while driving. In an Instagram video, Sian said: "So dangerous and most of us don’t know about it!"
The mum-of-one said she often found herself yawning and feeling tired on car journeys lasting over 30 minutes, especially if they involved a motorway. Describing it as a sensation of "uncontrollable tiredness", Sian soon realised it was a setting in most modern cars that was causing her problems.
The radio host said: "When you've got air conditioning in your car, you've got two buttons, and there's one that shows a car with arrows—the recirculation button. A lot of us were told that it would save energy if you put that on because it recycles the air inside your car, and it cools down quicker - that's true.
"However, apparently, it's not designed to be left on, and it can cause drowsiness. So I thought, right, this could be a load of nonsense, but if I get into my car and that button is on, it might be why I'm getting tired.
"I go in my car and, sure enough, that button is on. I turned it off, and I did a three-hour motorway journey the other day - didn't feel tired once."
People tend to feel the benefit of the recirculation button during extreme weather, as the car can quickly cool or heat the main car cabin without pulling in fresh air from outside. But without letting fresh air into the car cabin, people become exposed to more carbon dioxide, and in a confined space, that is what causes drowsiness - even if you've had a full night's rest.
Posting on Instagram, Dr Christabel Akinola claimed drivers should "never leave the recirculation button on for more than 20 minutes at a stretch". She said regular, fresh air is "essential" and warned drivers who feel sleepy for no explainable reason to "pull over" and make sure it's not the car's air quality.
A 2018 study titled "Carbon dioxide accumulation inside vehicles: The effect of ventilation and driving conditions" found that using the recirculation setting is the primary cause of high CO2 levels in car cabins. While short commutes typically do not exceed a concerning 2,500 ppm, prolonged trips and multiple occupants significantly increase the risk of elevated concentrations.
