One in 10 people is a "secret smoker" who tries to keep their habit hidden, a survey suggests.
For many people, smoking is a clandestine affair
The poll of 4,000 adults, commissioned by Boots, found 52% of smokers had kept their habit secret from their parents, even into adulthood.
Three out of 10 of smokers had lied to their GP, and a quarter had kept it concealed from their employer.
A third admitted lying to their family, who believed they had given up or had never smoked at all.
Angela Chalmers, a pharmacist at Boots, said: "Not many people realise that those one or two crafty cigarettes a day can still cause long-term damage to your health.
"Higher levels of carbon monoxide in your bloodstream means less oxygen is getting round your body.
"This can result in tiredness, breathlessness and headaches as well as making your skin appear dull and more prone to wrinkles.
"It can also affect the elasticity of the lungs, meaning you are putting yourself at risk of asthma and ageing your lungs well beyond your years."
The research found that smokers in London were most likely to keep their habit secret, closely followed by those in Yorkshire.
Seven out of 10 "secret smokers" admitted that they would like to give up for good this year
From July this year smoking will be banned in public places across the whole of the UK.
Amanda Sandford, of the charity Action on Smoking and Health, said: "It is understandable that smokers - particularly those who have tried to give up before and failed - might feel guilty about their smoking.
"But denying their habit won't help and they may find it harder to give up."
'Up to you'
Neil Rafferty, of the smokers' lobby group Forest, said he had known of many smokers who had hidden their habit.
"I always felt sorry for them. It's another example of how those in authority are determined to make us all feel like naughty children.
"But the truth is everyone is well aware of the risks, so if you want to smoke it's up to you.
"Smokers, secret or not, should not allow themselves to be browbeaten and chastised like this.
"As long as you're not deliberately bothering anyone else you have nothing to feel guilty about.
"It's your body and your life and you should tell the health freaks to butt out."