One in four Hong Kong teenagers has smoked, and second-hand smoke can aggravate respiratory symptoms even among smokers. These are the main findings of a University of Hong Kong study published in the latest issue of the journal Pediatrics. Researchers from the university's school of public health said the study was the first to show that exposure to second-hand smoke was associated with increased risk of persistent respiratory symptoms among adolescent smokers. Current smokers who were exposed to second-hand smoke at home for five to seven days a week were 77 per cent more likely to suffer from respiratory symptoms than those who were not exposed, researchers said. If they also encountered second-hand smoke outside home, the percentage of risk was even higher, at 85 per cent. Some 32,506 people aged 11 to 20 were recruited from 85 randomly selected schools in 2003 and 2004 and asked to fill in a questionnaire. The survey revealed 24 per cent had smoked - 9 per cent who were currently smoking, 13 per cent who had tried smoking and 2 per cent who had kicked the habit. More than 85 per cent said they encountered second-hand smoke outside home, whereas 51 per cent reported the same situation at home. One in 10 non-smokers said they had suffered persistent respiratory symptoms for more than three months in the past year. The rate doubled among smokers, with 22.2 per cent reporting the symptoms. If teenagers often encountered passive smoking, the risk of suffering from persistent respiratory symptoms increased 12 per cent and 25.9 per cent respectively for non-smokers and current smokers. Professor Ho Sai-yin, who led the study, said the finding was significant in shaping government policies. Some people argued that smoking should not be banned in restaurants if all waiters smoked, but this study proved that second-hand smoke was harmful to even smokers, he said. Meanwhile, 200 academics and health professionals attended a conference on tobacco control yesterday at the Academy of Medicine in Wong Chuk Hang. Dr Huang Jiefu , the mainland's vice-minister of health and director of the Chinese Association on Tobacco Control, said smoking was still common on the mainland and 40 per cent of surgeons were smokers. While Hong Kong spent HK$50 million on tobacco control each year, the central government only allocated 2.6 million yuan (HK$2.95 million), he said. The city's Tobacco Control Office had 140 staff, but the mainland's only had three. 'But that does not imply the central government is not determined to curb smoking,' he said. Smoking would be banned in the Ministry of Health next year, Huang said, and then in hospitals and schools in 2011. Secretary for Food and Health Dr York Chow Yat-ngok said that although the city's smoking rate had declined in recent years, not many young people and women had quit, so future campaigns would target these groups.