Smokers are becoming de-sensitised to a repetitive use of the same graphic health warnings on cigarette packs - according to researchers presenting at the British Thoracic Society Winter Meeting.

The research showed that the longer people are exposed to the graphic health warnings on cigarette packaging, the more their sensitivity and engagement with them are reduced.

But warnings that were lesser known - such as the threat of blindness from smoking - had a much higher deterring impact.

The study, led by academic Culadeeban Ratneswaran, from Guy's and St Thomas' Hospital, London, investigated the effects of long-term exposure of graphic health warning labels (GHWL) to people's sensitivity to the messages in both London and Singapore residents.

Singapore has used graphic health warnings for 5 years longer than the UK, so the study sought to compare the relationship between length of exposure and desensitisation.

The study involved 266 participants, 163 from London (56 smokers), and 103 from Singapore (55 smokers).

The results were clear; both smokers and non-smokers in the Singapore sample reported lower levels of disgust when viewing the warnings and they were significantly less likely to pay any attention to the messages when compared to London. In all, Singaporeans felt graphic health warnings were less of a deterrent than the UK group.

The UK sample had a statistically higher awareness of how smoking increases the risk of heart disease, mouth and throat cancer and lung cancer, but UK smokers had a significantly lower awareness of the effect of smoking on the risk of blindness.

Health risks such as blindness were thought to produce an increased response in both the UK and Singapore samples due to their low knowledge score and high emotional impact. Blindness was the least well-known consequence of smoking overall, despite being ranked ahead of mouth and throat cancer, heart disease and even stroke as the most deterring consequence.

The researchers conclude that reduced sensitivity to graphic health warnings may be a result of extended exposure.

In a previously published paper, which was supported by the British Lung Foundation, the impact of the warnings was found to be lowest among smokers with chronic obstructive pulmonary disease (COPD), a progressively disabling collection of severe lung conditions, including bronchitis and emphysema.

Culadeeban Ratneswaran, Honorary Research Fellow at Guys and St Thomas' Hospital, London, which is part of King's Health Partners said:

"Graphic health warnings on cigarette packs have played an important role in communicating important messages about the dangers of smoking. Our research shows that this effect may wane over time and that both visuals and messages need to be refreshed to make sure they retain a preventative impact.

We've shown that warnings with a low knowledge score that have a high emotional impact, could work best. "

Dr Sanjay Agrawal, lung specialist at University Hospitals of Leicester NHS Trust and Chair of The British Thoracic Society's Tobacco Specialist Advisory Group, said:

"The study shows the need to engage with the public in new and innovative ways about the huge range of dangers caused by smoking.

1 in 2 regular smokers die from their habit, so it is imperative we keep communicating - for the sake of this generation and the next.

The proposed roll out of plain cigarette packs will help to increase the impact of health warnings and reduce their brand appeal, to young people especially. This aspect should be part of a wider comprehensive tobacco control strategy involving national education campaigns, the provision of well-funded stop smoking support services, and other pivotal policies such as banning smoking in cars with children."