A new law that bans smoking in cars when children are present comes into force in Scotland this week.
Anyone caught breaking the law by smoking in private vehicles with someone under 18 on board faces an on-the-spot penalty of £100 or a fine of up to £1,000 if the case goes to court.
Smokers' group Forest has branded the regulations "patronising and unnecessary".
But health campaigners welcomed the move as they pointed to figures suggesting around one in six 15-year-olds are being exposed to second-hand smoke in the car.
Sheila Duffy, chief executive of anti-smoking charity Ash Scotland, said: "We know from speaking to parents that they want to protect their children from tobacco smoke, but often don't know enough about how smoke is harmful and lingers in the air even after you can't see or smell it.
"This legislation sends a clear message that children should grow up in a smoke-free environment, and who could disagree with that?"
The Smoking Prohibition (Children in Motor Vehicles) (Scotland) Bill, introduced by Liberal Democrat MSP Jim Hume, was passed unanimously by the Scottish Parliament in December last year and comes into force on Monday.
It was introduced to protect young people from the harm caused by second-hand smoke, which can cause serious conditions such as bronchitis, pneumonia and asthma.
Latest research shows the toxic particles in second-hand smoke can reach harmful concentrations within a minute of lighting a cigarette in a car, ministers said.
The Scottish Government said the measure is part of its plans to create a "tobacco-free generation" by 2034, defined as a smoking rate of less than 5%.
Public Health Minister Aileen Campbell said: "It's simply not safe to smoke when a child is in the car. Dangerous levels of chemicals can build up, even on short journeys, and 85% of second-hand smoke is invisible and odourless so you can't always see what they're breathing in.
"We know for a fact that the poisonous chemicals in second-hand smoke are extremely damaging to our health. We also know that children breathe faster than adults, meaning they ingest more of the deadly toxins."
The Scottish Liberal Democrats said the legislation would protect thousands of young people each year from second-hand smoke.
Mr Hume said: "It fills me with great pride that through hard work and cross-party consensus, we are now seeing the introduction of a law which can potentially save 60,000 children a year from the hazards of second-hand smoke."
Irene Johnstone, head of the British Lung Foundation in Scotland, said: "This new law will not only help reduce the exposure of second-hand smoke, but will also go a long way in helping Scotland becoming a tobacco-free generation."
However, other campaigners have criticised the new law.
Simon Clark, director of the smokers' group Forest, said: "The regulations are patronising and unnecessary. Very few adults smoke in cars with children. Smokers know it's inconsiderate and the overwhelming majority don't do it.
"So few people smoke when there's a child in the car it will be like looking for a needle in a haystack."
A law banning smoking in vehicles carrying children came into force in England and Wales in October last year.