Smokers may defy the health warnings by telling themselves their habit makes them look cool.

After all, sex symbols James Dean and Humphrey Bogart were rarely seen without a cigarette.

However, the latest evidence shows that smoking actually makes you less attractive to the opposite sex.

Telltale wrinkles from puffing on a cigarette may be to blame for people judging non-smokers to be better-looking, reports Daily Mail.

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This was the result of a study asking more than 500 people to pick the most attractive of twins where one smoked and the other did not.

Men found female non-smokers the most attractive in two-thirds of cases, while women chose non-smoking men as the most attractive 68 per cent of the time.

Professor Ian Penton-Voak, a co-author of the study from Bristol University, said: "People hypothesise that smoking causes damage to the skin and appearance, but this is a really neat way at looking at it because these twins are genetically identical so we can control for genetic factors involved in ageing.

"Appearance seems to be important to people, especially young people, so we could use these sort of findings as a basis for future interventions to stop people smoking."

Smoking can speed up the normal ageing, even after only a decade. Nicotine causes narrowing of the blood vessels in the outermost layers of the skin, while the chemicals in tobacco smoke damage collagen and elastin, fibres which give the skin its elasticity.

The wrinkles this causes are added to by facial expressions made when smoking — such as pursing the lips when inhaling or squinting to keep smoke out of your eyes.

Images were shown to more than 500 people who judged the more attractive sibling. Photo / Daily Mail
Images were shown to more than 500 people who judged the more attractive sibling. Photo / Daily Mail

To test if smokers did look worse, the researchers asked more than 500 people to pick the smoker and non-smoker from 23 sets of twins.

After finding smokers were easily identified, they created prototype pictures to make sure the twins' facial expressions or poses could not alter the results.

Using these images, tweaked by a computer to standardise how smokers and non-smokers looked, they asked which people found "more attractive".

The results show men and women both found the opposite sex more attractive when they did not smoke.

But women also judged other females who did not smoke as more beautiful in 70 per cent of cases, while men thought non-smokers of their own sex were better looking 72 per cent of the time.

The researchers state: "Our results provide evidence that smoking may negatively impact facial appearance, and that facial appearance may provide information about smoking status."

They say the "social stigma" of looking worse from smoking could therefore encourage people to quit, adding: "One type of smoking behaviour change intervention targeted at young people is the use of applications illustrating the changes in facial appearance likely if they age as a smoker and a non-smoker.

"These work on the basis that young people are particularly sensitive to the potential negative effects smoking has on their attractiveness as they age."

A survey of smokers in 2014 found vanity was more important to them than the impact on their health.

Asked about their health concerns, most said they were more worried about their looks than whether they might die or be disabled by cancer or heart disease.

Their biggest concerns were discoloured teeth, followed by bad breath, wrinkles, fine lines and yellowing nails, according to the poll by an electronic cigarette firm. The latest study is published in the journal Royal Society Open Science.