Smoking causes damage to skin right across the body, a study has suggested.
Dermatologists say the study shows smoking damages skin
Research in Archives of Dermatology observed the effect by looking at the upper part of the inner arm in smokers and non-smokers.
Previous studies have focused on the face, where skin can also be damaged by exposure to the sun.
But the University of Michigan, Ann Arbour, team say this study shows smoking alone makes the skin age, which may help persuade some to quit.
The researchers photographed 82 people's upper inner right arms.
Participants were aged 22 to 91. Such a wide age range was used in order to record the natural state of old and young skin.
Half of those studied had a history of smoking and had smoked, on average, for 24 years.
The number of packs of cigarettes they smoked ranged from a quarter of a packet to four packs per day.
The team created a nine-point scale to measure damage to skin which is not exposed to the light.
In those aged over 65, there was almost a two-point difference between smokers and non-smokers.
In the over-45s, the difference was around a point.
Writing in Archives of Dermatology, the researchers led by Dr Yolanda Helfrich, said: "We found that the number of packs of cigarettes smoked per day, total years of smoking and pack-years of smoking [an average of packs per day over the number of years of smoking] were correlated with the degree of skin aging.
"After controlling for age and other variables, we found that only packs of cigarettes smoked per day was a major predictor of the degree of photo-protected skin ageing."
Evidence 'mounting up'
Dr Helfrich said: "Previous studies have shown that smokers have a greater degree of skin ageing, but those have looked at facial skin.
"There are some sceptics who said the sun was having some of the effect.
"We have demonstrated that there was a significant degree of damage just from smoking."
She added: "The evidence is certainly mounting up that smoking is not good for you. This just adds to all of that."
She said more research was needed to show exactly how smoking damaged the skin.
Indy Rihal, of the British Skin Foundation, said: "In addition to UV light from the sun and sun beds, cigarette smoke is a main environmental factor that causes changes in the skin often associated with 'looking old' such as coarse wrinkling and a sallow, leathery texture.
"There is strong evidence suggesting cigarette smoke has a negative effect on the appearance of skin.
"Smoking enhances an enzyme in the skin, matrix metalloproteinase-1, resulting in increased collagen breakdown and diminished collagen production. The overall effect causes wrinkling and inelasticity.
"In addition the constriction of tiny blood vessels in the skin caused by smoking reduces the oxygen supply to the skin negatively affecting skin health and appearance in general."
Amanda Sandford, of Action on Smoking and Health (ASH) said: "This study provides further evidence of the detrimental effects that smoking can have on the skin.
"No amount of anti-ageing cream will remove the wrinkles caused by cigarettes so the best way for smokers to avoid the wrinkled prune look is to stop smoking."