The British Medical Association (BMA) has made an announcement saying that smoking should be banned in cars.
This would be to protect people, especially children, from other people's smoke.
There is already a ban on smoking in public places and the BMA says this should include cars.
The evidence from their research shows that levels of poisonous chemicals in cars are up to 23 times higher than other places where people smoke.
This is because when the windows are closed there is nowhere else for the smoke to escape from the car, so it floats around.
But the government has said it would be difficult to enforce a ban. In other words, it would be difficult to know if people were actually sticking to the law.
Smoking is already banned in taxis and other vehicles used for people's work.
The arguments about this have been going on for a long time.
In 2010, one doctor said that parents who smoked in front of their children were "irresponsible".
"At school we were talking about the smoking story. All of my class think it should be banned, except for two people who said no because their mums smoke in cars. Even my teacher Mrs Johnson thinks it should be banned."
Emily, 9, Essex, England
"Smoking in cars should be banned because it affects the well-being of the passengers in the car. In school we had a debate whether it should be banned or not... and 25% of us voted that it should be banned!!"
Taylan, 10, Wales
"Although I would personally like smoking to be banned in cars and everywhere else, I know that a law like that would never be upheld as too many people would disobey it. Maybe the law could be more flexible, and a fine could be given to those who smoke in their cars without the windows open?"
Daisy, 13, Leicester, England
"It's their property and I don't think it should be banned, although I think you should warn them about the dangers of smoking in the car, especially when children are there too."
Meg, 13, England
"No! I don't think it should be banned because it's just invading people's private lives! They should be able to smoke whenever they like in their own cars. It's bad, but it's their choice and no-one else's."
Alisha, 13, Falkirk, Scotland
"I think it should definitely be banned. Especially if whoever is smoking is with a baby in the car, because babies have sensitive lungs and it's not good for them to breath in the smoke. Plus it smells horrible if you're in a small space like a car."
Alicia, 10, London, England
"I think they should ban smoking in cars to prevent children from suffering from passive smoking. I don't like the smell of the smoke. I'm glad that my mum and dad don't smoke."
Emily, 9, Scotland
"I think they should ban smoking in a car because the smoke can cover the window with smoke and block the driver's view. People say smoking in a car shouldn't be banned because 'It's their car, so they can do anything they want'. But I disagree because health and safety is more important than smoking in a car."
Ibraheem, 11, London, England
"Well, I don't think that smoking in cars should be banned because it would be hard to enforce that law if it was put in place, and the cigarette lighters in cars would be put out of their primary use. But I'm sure the government will make the best decision they can!"
Ted, 12, York, England
"Adults know that smoking can give you cancer so why do it? You also shouldn't smoke in the car because it can put you off your driving and can cause an accident."
Sophie, 10, Sussex, England
"I think that smoking should be banned altogether and especially in cars where there are children. It's bad for their health. And just because parents are ruining their own health, they don't need to damage their kid's health too!"
Sarah, 12, London, England
"I think they should stop it and make people pay a fine if they are found smoking in a car as it's not only bad for them, but bad for everyone around them... ESPECIALLY in such a confined space like a car."
Laura, 12, Stockton-on-Tees, England
"I think they should ban it because if another person is in the car with them, it will affect their health too. Anyway, you shouldn't smoke in the first place!"
Indie, 12, Preston, England
"People who say 'it's my car, it's my choice' have an irresponsible attitude for smokers. YOU might not mind the stink of the car, but kids get harmed by the toxic chemicals. Plenty of children also get teased at school because they smell of tobacco, and even if you are alone in the car, you're not focused, because your hand is off the wheel. It pollutes the air if you open the window and the fumes could still linger for ages afterwards, which children would have to cope with."
Elizabeth, 11, Newcastle, England
"I think smoking in cars should be banned because...firstly, everyone in the car will breathe it in. Secondly, if you were to have a crash and drop the cigarette then the car could set alight. And lastly... it's just wrong!"
Charley, 11, Birmingham, England
"I don't like smoking at all, but I don't think it should be banned in cars. It's up to you if you want to smoke in your car and it's up to you if you want to smoke around your children. However, I do think that people who do smoke around children should be aware of the harm it has on them."
Ella, 13, Manchester, England
"I really wish there was a ban. I sit in the car all the time breathing in my parent's smoke and I don't like it, but no one listens to kids!"
Sarah, 14, Bradford, England
"I think they should ban smoking in cars because it isn't very nice seeing children having to breathe in the nasty chemicals. Also some of my friends have told their parents to stop smoking full stop and they just turn round and go mad and say... 'it's my life, not yours'!"
Mikayla, 14, Dorset, England
"I don't think you should ban people smoking in cars because it's their car and they can smoke in there if they wish. Also, it would be very hard to stop people smoking in their car because you can't see what they're doing. Also, if a parent was that scared that their kid would have something wrong with their lungs they wouldn't smoke or let anyone smoke around them!"
Abbie, 11, London, England
"Smoking in cars doesn't just affect the adult it affects the growth of children which can also affect their health. I think it should be banned."
Lucy, 13, England
"I don't think you should be allowed to smoke if a child who is under the age of 15 is in the car as it isn't good for their health."
Aliya, 11, Northampton, England
"Smoking should be banned in cars because it is the worst thing you can do for yourself and the people around you. I can't even stand the smell if I walk past a smoker let alone sit in the same car as them!"
Anna, 13, Surrey, England
"I don't think people should be banned from smoking in their own cars because it's their property, just like a house."
Harrison, 13, Portsmouth, England
"I think that smoking in cars should be banned because it is just the same as smoking in a restaurant."
Hannah, 11, London, England
"I think It shouldn't be banned because my mum and dad smoke and they have not had one accident and if you are affected by the fumes then you can always turn on the air conditioning and put the windows down."
Steven, 15, Scunthorpe, England
"I think that smoking should be banned in cars when there are children and small babies in the car."
Kelsey, 13, Luton, England
"It should be totally banned! It's awful, disgusting and it pollutes the air. I have to hold my breath whenever I pass someone who's smoking because the smell makes me feel sick. I can't imagine what it must be like for babies and kids who have to ride in a car with the smoke floating around everywhere."
Ana, 13, Northampton, England
"Smoking should be against the law. Not just when driving but all the time!"
Olivia, 11, Essex, England
"I think they should stop smoking, I have asthma and its twice as bad for someone with asthma then a normal person. Its bad enough that my lungs are bad but when people are smoking around me then I get chemicals in my lungs too. It can affect passengers and It's selfish but most people who smoke don't see it like that."
Danielle, 13, Staffordshire, England
"I think that smoking should be prevented in cars because it can disturb the driver's concentration and is similar to being on the mobile phone whilst driving (which has already been banned)."
Liberty, 13, Hethersett, England
"I think it should be stopped because it's not fair on the children in the back of the car who inhale the smoke, and it could damage them in later life."
Charles, 13, London, England
"I don't think smoking in cars should be banned because it's your parents decision if they want to smoke. So the law can't really stop them if they are smoking, otherwise if we had the police looking out for every smoker then they wouldn't be able to stop real crimes."
Jake, 14, Wiltshire, England
"Some people are asthmatic and the smoke will interfere with their asthma. For a start, I am asthmatic and when my father smokes it interferes with my asthma. Even for people who don't have asthma, smoking will interfere with their lungs so that's why they shouldn't smoke in cars or anywhere else."
Nishat, 9, London, England
"I think smoking should be banned from cars because secondhand smoke is harmful to small children, the passenger and the driver too. Cigarette smoke gives you a higher risk of cancer, so adults should think before they smoke for their own and their children's health."
Devin, 10, Ireland
"I think that it should be banned as smokers are putting their children, and in some case babies, at risk. It can affect their future if they are exposed to it from an early age."
Andrew, 14, Hampshire, England
"I think it should be banned because it can endanger our health and make a really bad smell in the car. It would be better if people who smoke in cars were to be fined for doing it."
Claudia, 14, Jakarta, Indonesia
"I tell my mum and dad to stop but they say "it's my car, so I can!". I'm sick of it! I just want to be healthy! It should definitely be banned in cars."
Shantell, 14, York, England
"I think that people should ban smoking in cars because if they have a child with them it could give them breathing problems when they're older. It also pollutes the air."
Violet, 11, Lincoln, England
"It would be hard to ban it, but i think it's irresponsible to smoke in your car if you have child passengers."
Elena, 13, Belgium
"We have just discussed this as a class and the majority think that smoking in cars should not be banned because it is your car so your choice. Others think that it should be banned because smoking prevents you from having two hands on the driving wheel."
Cory, 15, Bridgend, Wales
"Smoking is gross. Why isn't it illegal?!"
Shaquana, 13, London, England
"This is horrible, I would refuse to get in a smoker's car until the fumes had been cleared! It is also dangerous as smoke can block the window preventing you from seeing out."
Adil, 12, Crawley, England
"Smoking should be banned in cars because it can affect passengers via second hand smoking. The smoke could also distract people and cause an accident."
Tamzin, 11, Sheffield, England
"Yes it should be banned in cars because it is damaging to children's lungs and the smell is awful."
Rosie, 14, Bridgend, Wales
"I think that the ban should come in to prevent children having problems with their lungs when they are older."
Kazimiera, 12, England
"I think that they should stop people from smoking in cars because if there was a baby in the car with you then the smoke could affect the child."
Tilly, 13, London, England