A new study links second-hand smoke to hearing loss in children.
Some 1,500 teenagers were given hearing tests in the study. They were also tested for cotinine, which is produced when nicotine is metabolized, so it's a good marker for exposure to tobacco smoke.
"What we found was that the higher the level of cotinine in their blood - and thus the higher the level of exposure to second-hand smoke - there was greater prevalence of the hearing loss," says Dr. Anil Lalwani of New York University Medical Center, who conducted the study.
In conducting the study, Lalwani wanted to extend what was known about the association between second-hand smoke and the ear. For example, children exposed to tobacco smoke get more ear infections.
"We also know that adults who smoke have an earlier hearing loss than adults who do not," Lalwani says. "And this made us wonder whether early exposure to second-hand smoke that children would be exposed to, is that also deleterious to the auditory system?"
Most of the 12- to 19-year-olds in the study who had measurable hearing loss weren't aware of it. They might miss things in class and not hear instructions. Lalwani says the loss could be enough to be causing real harm.
"Kids who have second-hand smoke exposure have behavioral issues as well as cognitive issues. So it's quite possible that even this mild hearing loss that these children might have may be impacting their development in school."
Why hearing is affected by second-hand smoke remains a bit of a mystery. Lalwani suggests it may be because of known effects of tobacco smoke on blood vessels, possibly compromising the flow to the inner ear. Another possibility is a toxic component of the smoke acting more directly.