UK drivers warned button inside car causes drowsiness if not turned off

Drivers have been issued a warning over the button found in modern vehicles

20:34, 13 Apr 2026

Drivers have been issued a warning over the button(Image: Getty Images/Maskot)

Motorists are being warned about the dangers of leaving a seemingly simple setting switched on in their vehicles for long trips.

Failing to switch it off could lead to a feeling of "uncontrollable tiredness" behind the wheel[1], which can quickly become a serious problem, reports Express.co.uk.

Most modern vehicles[2] are made with an air recirculation button, which blocks outside air from entering the vehicle while keeping the internal air circulating.

Get breaking news on BirminghamLive WhatsApp[4], click the link to join

It can prove useful for cooling down during the summer months, conserving fuel, and blocking out pollution and unpleasant odours when stuck in traffic[5].

But leaving this setting on for more than 20 minutes can prove hazardous, as it drains oxygen levels and raises carbon dioxide (CO2) levels, which can lead to drowsiness and impair concentration.

Capital Breakfast and ITV's This Morning presenter Sian Welby found out the risks first-hand.

The 39-year-old revealed that it was only while casually browsing TikTok that she made the connection between the car[6] button and a problem she had frequently had while on the road

In an Instagram video, Sian said: "So dangerous and most of us don't know about it!"

The mum-of-one admitted she regularly found herself yawning and feeling fatigued on car[7] journeys lasting more than 30 minutes, particularly on motorways.

Describing the sensation as "uncontrollable tiredness", Sian quickly established that a setting found in most vehicles was the cause of her problem.

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."

Drivers tend to notice the advantages of the recirculation button during extreme weather conditions, as the vehicle can rapidly cool or heat the cabin without drawing in outside air.

Yet without allowing fresh air into the car, occupants become increasingly exposed to carbon dioxide, and within such a confined space, this is precisely what triggers drowsiness -- even following a full night's sleep.

In an Instagram post, Dr Christabel Akinola advised drivers to "never leave the recirculation button on for more than 20 minutes at a stretch".

She said that regular, fresh air is "essential" and cautioned anyone feeling inexplicably sleepy behind the wheel to "pull over" and check whether the vehicle's air quality could be responsible.

A 2018 study titled "Carbon dioxide accumulation inside vehicles: The effect of ventilation and driving conditions" discovered that utilising the recirculation setting is the main cause of elevated CO2 levels in car cabins.

While brief commutes generally do not exceed a concerning 2,500 ppm, extended journeys and multiple passengers significantly increase the risk of elevated concentrations.

References

1. ^ wheel (www.birminghammail.co.uk)
2. ^ vehicles (www.birminghammail.co.uk)
3. ^ New number plate changes now in effect with GBP1,000 fines for drivers (www.birminghammail.co.uk)
4. ^ BirminghamLive WhatsApp (chat.whatsapp.com)
5. ^ traffic (www.birminghammail.co.uk)
6. ^ car (www.birminghammail.co.uk)
7. ^ car (www.birminghammail.co.uk)