Inhaling dangerous chemicals in cigarettes, including arsenic and cyanide, damages major organs and increases the risk of stroke and dementia, a new stop-smoking campaign will warn.
The Smokefree Health Harms, launched by Public Health England, will warn smokers the chemicals they inhale move through the heart, the lungs and into the bloodstream, finally damaging cells in the brain.
England's chief medical officer, Professor Dame Sally Davies, said: "We know about the serious effect smoking has on the heart and lungs but smokers need to be aware of how much potential damage is being done to the brain and other vital organs through toxins in cigarettes entering the blood.
"Smoking is the major cause of premature death, with one in two smokers dying prematurely from smoking-related diseases, and it is extremely worrying that people still underestimate the health harms associated with it.
"However, it is not all doom and gloom for smokers looking to quit this New Year. Within five years of stopping smoking, your risk of stroke can be reduced to the same as a lifetime non-smoker."
Dr Gareth Hagger-Johnson, research associate at University College London (UCL), said: "Accelerated decline in cognitive reasoning and memory is more advanced in smokers, with one of our studies at UCL showing it to be nearly 38% faster in persistent male smokers compared to non-smokers.
"The decline in the brain's cognitive powers is naturally seen with ageing but there are a number of identifiable risk factors, including smoking and heavy alcohol consumption, which can be associated with an accelerated rate of decline."
Professor Kevin Fenton, director of health and well-being for Public Health England, said: "More than eight million people smoke in England. With half of long-term smokers dying prematurely from a smoking-related disease, highlighting the unseen damaging effect smoking has on the body's major organs provides a real motivation for people to stop."
Joe Korner, director of external affairs at Stroke Association, said: "Stroke is a major cause of death and adult disability in the UK and you are twice as likely to have a stroke if you smoke. The more you smoke, the more your risk increases."