A study of more than 1,500 U.S. teens aged 12 to 19 suggests that second-hand tobacco smoke can greatly damage their ears, the BBC reports. While it isn’t clear exactly how much exposure incites damage, they say smoke can increase the risk of middle ear infections and could harm blood supply to the ear. The greater the exposure, the greater the damage, they say. In the study, about 40 per cent of 800 teens who were exposed to second-hand smoke had detectable hearing problems, while about 25 per cent of 750 teens did who weren’t exposed. Even so, less than a fifth of them knew they had a problem, because mild hearing loss is often not noticeable to the individual.