Experts have long debated the most common cause of tinnitus — a ringing, whooshing, roaring, or hissing in the ears without an external sound source. Some have maintained that tinnitus is triggered by hearing loss: with less sound coming in, the brain compensates by becoming hyperactive and generating a phantom noise.

But that theory hasn’t explained the problem for people with normal hearing tests who still have tinnitus. What causes tinnitus in those cases?

Mounting evidence

Increasingly, Harvard Medical School scientists are finding evidence that some people have “hidden” hearing loss: damage to the auditory nerve — which carries sound signals from the ear to the brain — that isn’t picked up by conventional tests.

Researchers first discovered the phenomenon in lab mice in 2009. “From there, it wasn’t difficult to add two and two by suggesting that the loss of these nerve fibers in people with normal hearing tests could be associated with tinnitus,” says Stéphane Maison, a tinnitus researcher and associate professor of Otolaryngology–Head and Neck Surgery at Harvard Medical School.

Subsequent studies began making the connection. The latest — believed to be the largest and most nuanced to date — was published Nov. 30, 2023, in Scientific Reports. Maison and his colleagues at Harvard-affiliated Massachusetts Eye and Ear recruited almost 300 people (ages 18 to 72) with normal hearing tests who had chronic tinnitus, no tinnitus, or intermittent tinnitus.

Scientists measured participants’ auditory nerve responses and brainstem activity. Compared with not having tinnitus, having chronic tinnitus was associated with a loss of auditory nerve fibers as well as increased brain activity. “That fits with the idea that as a result of hearing loss, the brain increases its activity, which is possibly why you perceive a tone or a sound that isn’t there,” Maison says.

What this means for treatment

For people with measurable hearing loss, getting hearing aids sometimes reduces the perception of tinnitus. But hearing aids aren’t recommended for people with normal hearing test results — even if your doctor suspects hidden hearing loss — since we don’t have tests outside of research labs to measure it.

Still, the new evidence linking hidden hearing loss and tinnitus offers hope for people with tinnitus. “When you have hidden hearing loss, only a portion of the auditory nerve has degenerated. Another portion remains alive for years or decades. And a number of experiments by others have found that it’s possible to regenerate nerve fibers in animal models,” Maison says. “If we can one day regenerate those fibers in humans, perhaps it might bring back missing information to the brain, reducing its hyperactivity and the perception of tinnitus.”

Until that day comes — and it’s unclear when or if it will — we have only limited ways to cope with the problem.

What you can do

If you have tinnitus despite a normal hearing test, report it to your primary care doctor or ear, nose, and throat specialist. In rare cases, the noise can be caused by a tumor or cyst pinching the auditory nerve, a buildup of earwax, or blood vessel damage. Sometimes treating underlying conditions like these can reduce or even eliminate the noise.

More often, we can only learn to how to live with or reduce tinnitus. The following strategies may help.

Distract your brain. Listening to white noise or nature sounds might make tinnitus seem quieter. Use a white noise machine, sleep headphones, earbuds, or a wearable sound-masking device.

Use mind-body therapies. Cognitive behavioral therapy, mindfulness-based tinnitus treatment, and biofeedback can help you redirect negative thoughts and emotions linked to tinnitus.

Reduce stress. Stress may increase both your perception of tinnitus and your reaction to it. Try yoga or tai chi to help manage stress; since you’ll be concentrating on movement and breathing, you might not focus on the tinnitus as much.

Live a healthier lifestyle. Practice good sleep hygiene, exercise daily, and limit alcohol intake. Each one of those healthy habits can help reduce the frequency and intensity of tinnitus, and also reduce stress.

Consider trying bimodal stimulation. These new devices for home use provide two types of stimulation — for instance, sound along with gentle taps to the wrist delivered by a bracelet. “They aren’t yet widely recommended as there’s not enough evidence that they work, but preliminary results are encouraging,” Maison says. “Ask your physician about your options.”

Article originally appeared on Harvard Medical