Passive smoking raises the risk of impaired hearing in teenagers, a new study has warned.

Inhaling second-hand smoke almost doubles the chances of senso-neural hearing loss which results from problems affecting the inner ear, US-based scientists said.

Though the impairment is at a minimal level, it could affect the teenagers' performance in the classroom and their studies, the research found.

The study chose 1,500 children and teenagers aged between 12 and 19. They were given extensive hearing tests.

Their blood samples too were analysed for traces of a chemical substance called cotinine, the presence of which in the blood of a non-smoker is testimony to passive smoking.

Upon testing their ability to hear different frequencies of sound, the respondents who were exposed to second-hand smoke performed worse and were found particularly impaired in the mid-to-high frequency range crucial to understanding speech.

The results of the study were published in the journal Archives of Otolaryngology - Head & Neck Surgery.

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