Hearing tests conducted on a national sample of teenage girls and boys showed that now roughly 17 percent - or 1 in 6 - of teens of both sexes have hearing losses that can make it harder for them to hear speech and some high-pitched sounds.
"The girls have kind of just caught up with boys," study author Elisabeth Henderson of Harvard Medical School in Boston told Reuters Health.
Traditionally, boys were more likely to be exposed to loud noises from leaf-blowers, firearms, or work machines, Henderson noted - but today, more and more teens have portable music players, and both sexes are listening to loud music from headphones.
The kids who reported recent exposures were no more likely to show signs of hearing loss, but it's still possible that this increase in portable loud music is having an effect, perhaps explaining why girls have caught up to boys' levels of hearing loss, Henderson said in an interview.
To investigate whether the recent popularity of portable music players is affecting teens' hearing, Henderson and her colleagues looked at hearing tests collected from 2,519 teenagers between 1988 and 1994, and 1,791 teenagers between 2005 and 2006.
They considered three types of hearing loss: low-frequency loss, in which people struggle to hear sounds in the low end of the sound spectrum (such as parts of human speech); high-frequency hearing loss, which affects how well they hear high pitches (such as chimes or a microwave beep, or even kids' speech); and noise-induced hearing-threshold shifts, or "NITSs," in which people have trouble hearing sounds in the middle of the sound spectrum (which can include some human speech and higher-pitched sounds from musical instruments).
The investigators found that all three types of hearing loss were generally as common in the recent group of teens as they had been during the previous survey.
But when they looked more closely at the data, they saw that one group - teen girls - had experienced an increase in the rate of NITSs, from 12 percent in the first survey to 17 percent in the second.
Some form of NITS is permanent, and some is temporary, Henderson noted. "It's impossible to tell."
Henderson said she was not surprised they didn't find higher rates of hearing loss now that more teens are listening to music through headphones. That's because high-frequency hearing loss, for instance, comes only after years of exposure to loud sounds, so it would be unlikely in teenagers.
Even NITSs could become more common as teenagers age, she added. "It's possible that teenagers, as they become young adults, will have even more hearing loss."