AN AIR quality expert has warned drivers to be wary when using an everyday feature on the dashboard of their cars.
TikTok creator Thomas Morales shared a sombre video message to the platform which has now been viewed 1.8million times.
He captioned the 45-second clip: "Use this button in your car wisely..."
Thomas, who owns an air quality testing company, said he never thought twice before turning on his car's air circulation button.
That was until he decided to take one of his company's air sensors with him on a long drive up north to a cottage.
He said what he learned was "shocking".
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Thomas explained: "So we turned on the air circulation button and within 20 minutes the CO2 levels, carbon dioxide, which is what we breathe out, rose by five times within just 20 minutes.
"High CO2 levels isn't very healthy and can even lead to fatigue. Just imagine how high it gets on longer road trips with larger families.
"The more shocking thing is I could barely find anything about this online, so try to keep this car's feature to a minimum."
People may experience health effects in places where CO2 is elevated, according to the Minnesota Department of Health, but the symptoms are usually due to other contaminants in the air.
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The department said: "At high levels, the carbon dioxide itself can cause headache, dizziness, nausea and other symptoms. This could occur when exposed to levels above 5,000 ppm for many hours.
"At even higher levels ... CO2 can cause asphyxiation as it replaces oxygen in the blood-exposure to concentrations around 40,000 ppm is immediately dangerous to life and health.
"CO2 poisoning, however, is very rare."
Many who viewed Thomas' video said they had no idea of the dangers associated with using the dashboard button.
One user said: "Ohh goodness I use it all the time always thought it was better that way."
Another wrote: "I use it to get heat or A/C to the backseat passengers faster. Didn't realize I was KILLING EVERYONE ONBOARD."
But others were more sceptical about the legitimacy or gravity of Thomas' concerns.
One person commented: "this is fear mongering. cars are not sealed. there's plenty of O2 for days of driving with a whole family even if cars were sealed", to which Thomas replied: "O2 is not the issue I was referencing, but the accumulated CO2."
Someone else asked: "Is the level at 5x is even a concern? If it’s extreamly low 5x might still be very low. Lacking data here."
And another said: "It's a recirculation button. It's mainly used for a/c in the summer to gain cooler air in the vehicle. If not the condenser works harder."
It comes after a motors whizz, known as Chequanlaosi on , also warned against overusing the air circulation feature.
He said: "In the summer, the car will emit formaldehyde after being exposed to the sun.
"After we get in the car and turn on the air conditioner, we must turn on the outer circulation for 10 minutes, and then turn on the inner circulation after the formaldehyde is exhausted."
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Formaldehyde is used in heavy industry and for embalming but is known to cause cancer through long-term exposure and is toxic to humans.
In small doses, it can cause coughing, headaches, and eye irritation.