Printed labels on cigarettes featuring health warnings may not have much of an effect on smokers due to the brain's fear centre.

A study at the Universities of Bonn and Koln in Germany looked at smokers and non-smokers and their responses to different photographs.

They were shown fearful, happy and neutral faces while the activity in their amygdale was recorded and initially, there was no difference.

However, the scientists then asked the smokers to not have a cigarette for 12 hours before carrying out the test again.

It was found that the craving of nicotine had reduced the activity of the fear centre, making smokers indifferent to the fearful images.

Dr Ozgur Onur, the study's principal author, said: "It seems that they are mentally caught up in their addiction, resulting in a lowered receptivity for fear-inducing stimuli."

As such, he explained that shocking images of smokers' lungs and tumours on cigarette packs may not have much effect on smokers, as they are not receptive to them, even though they are likely to put non-smokers off further.

Pictorial warnings were introduced to printed labels on cigarettes in October 2008 in the UK.

Denny Bros Ltd, 14 July 2011