What's causing hearing loss for millions of Americans?

Millions of U.S. adults have some sort of hearing damage and a surprising number don’t even know it, according to a new report from the Centers for Disease Control and Prevention.

Hearing loss affects around 40 million adults — one in five between the ages of 20 and 69. It is the third most common chronic condition in the U.S. Almost twice as many people report hearing loss as report diabetes or cancer.

While lengthy exposure to loud sounds at a noisy workplace is a common culprit, the new report emphasizes that the routine noise of everyday modern life can damage hearing just as much.

“Forty million Americans show some hearing damage from loud noise, with nearly 21 million reporting no exposure to loud noise at work,” CDC Acting Director Dr. Anne Schuchat said in a statement. “This can be distressing for people affected and their loved ones.”

“What’s causing it is loud noise and it’s not just how loud the noise is, it’s how long someone’s exposed to it,” CBS News medical contributor Dr. David Agus told “CBS This Morning.” “A moderate noise for a long period of time can cause hearing loss.”

Common culprits include using a leaf blower, going to loud concerts, wearing earbuds and headphones, and even cellphone use.

The report also found that about one in four U.S. adults who say their hearing is good or excellent actually have some hearing damage.

“We’re learning now that the prevalence is higher than we thought and it’s really something we need to pay attention to,” Agus said.

So how loud is too loud? The answer is complicated. “Unfortunately we don’t know until it’s too late most of the time,” Agus said. “There’s no quantitative measure for it.”

He recommends not turning up music on your earbuds too high, limiting the use of power tools and using hearing protection in loud environments.

“Keep it to a lower level. Don’t really push it too high because if that damage happens to the nerves in your ears, we can’t regenerate new nerves there and it can cause a problem,” Agus said.

Experts say people concerned about their hearing should:

• Avoid noisy places whenever possible.

• Use earplugs, protective earmuffs, or noise-canceling headphones when they are around loud noises.

• Keep the volume down when watching television, listening to music, and using earbuds or headphones.

• Ask their doctor for a hearing checkup.