Exposure to secondhand smoke can lead to hearing loss in teenagers, who often don’t realize they have hearing difficulties, a new study suggests. Scientists conducting the study recommend that teens exposed to secondhand smoke be closely monitored for early hearing loss with periodic testing, HealthDay reports.

The researchers asked 1,533 nonsmoking teens about their exposure to secondhand smoke and whether they had any hearing problems. The teens were given hearing tests and underwent blood testing for cotinine, a byproduct of exposure to nicotine.

The study found that teens who were exposed to secondhand smoke were more likely to have both low- and high-frequency hearing loss, compared with teens who were not exposed. The more exposure they had, the more severe their hearing loss. Yet more than 80 percent of those who had hearing loss did not realize it, the researchers report in the Archives of Otolaryngology—Head and Neck Surgery.