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CROS and BiCROS Hearing Aids

What are CROS and BiCROS hearing aids?

Some people can hear very little in one ear—so much so that a standard hearing aid won’t help. 

If a sound occurs on the side of your bad ear, your head literally blocks the sound from reaching your good ear.  Audiologists call this the “head-shadow effect,” and it tends to affect consonants, the higher-frequency sounds important for understanding speech. In short, when you can’t hear from one ear, it will be especially hard for you to distinguish “cat” from “hat.” This is even harder in environments like restaurants and bars, which have grown noisier over time. Background noise is a problem for all of us, but worse if you have very little hearing in one ear, a condition called single-sided deafness (SSD) or unilateral hearing loss.    

Many people simply live with their hearing issue—just like many people choose to endure untreated hearing loss in both ears. They might ask people to speak to them on their good side. But that isn’t a complete solution. They’ll still struggle in restaurants or at a noisy event and have trouble locating the source of a sound.  

Fortunately, there are solutions, ranging from specialized headphones to hearing aids to surgical implants. When it comes to hearing aids, devices known as CROS and BiCROS are designed especially for single-sided deafness. 

What is CROS?

The acronym stands for Contralateral Routing of Signals. With a CROS system, you wear hearing aids on both ears, even though you can’t hear in one of them. The sound detected by the aid on the “bad ear” is transmitted directly to the aid on the “good ear” side. This gets rid of the “head shadow” effect.

“You are now hearing signals on both sides of your head all in one ear,” said Dr. Catherine Palmer, Director of Audiology and Hearing Aids at the University of Pittsburgh Medical Center and the President of the American Academy of Audiology.

CROS and BiCROS hearing aids are designed especially for people who have severe hearing loss in one ear.

What are BiCROS hearing aids? 

BiCROS are very similar to CROS hearing aids, except they’re designed for people who have hearing loss in their “good” ear, too. 

With a BiCROS system, the aid in your better ear will also be programmed for any amplification you may need. The “Bi” stands for Bilateral.  

How is CROS different from other hearing aids?

Traditional hearing aids send sound into the ear they are sitting on. With a CROS set up, the device on the non-hearing ear looks like a traditional hearing aid. But “it is really a microphone and transmitter and is picking up the sound to send it to the device on the hearing ear,” Palmer explains.  

Who is a candidate for CROS and BiCROS?

You are a candidate if one of your ears is particularly bad or has no hearing at all. About 60,000 people in the United States develop this problem every year. The cause might be a viral infection, getting hit on the head, a shortage of blood to the auditory pathway, or a benign tumor, called an “acoustic neuroma,” on the nerve that connects the ear to the brain.

Another cause is Ménière’s disease, when fluid builds up in part of the inner ear. For example, teacher Carly Sygrove, shared her story of single-sided deafness most likely associated with Ménière’s disease. While she tried a pair of CROS hearing aids, she said she is still deciding on a treatment option.

“If you notice a loss in one ear or both ears, the first thing you want to do is schedule an appointment with an audiologist or ENT [ear nose and throat doctor] so they can evaluate your hearing and identify the cause of the problem,” notes Palmer. 

If you suspect a medical cause for your hearing loss, promptly see an ENT doctor (also called an otologist). You may need laboratory testing to rule out inflammatory or infectious causes. If you lost your hearing suddenly, you may be advised by an ENT to take steroids.

If your condition can’t be treated medically, your next step is to speak to an audiologist about your options, including CROS and BiCROS. Similar to standard hearing aids, CROS and BiCROS can operate on batteries or are available as rechargeable devices.

Alternatives to CROS and BiCROS

If you have normal hearing in your good ear, or close to it, you may dislike wearing a hearing aid in that ear, says audiologist Daniel R. Schumaier, who is also president of Ear Technology Corporation, in Johnson City, Tenn. To address that problem, he created TransEar, which is very much like a behind-the-ear hearing aid. 

In the bad ear, you’ll wear a custom shell that fits in the ear canal. It contains a miniature oscillator, which touches the bone. Sound waves turn into vibrations that drive the oscillator, which transfers the signal through the bone to the cochlea in the opposite ear.

Bone-anchored hearing systems and cochlear implants

If you have single-sided deafness and another problem—like chronic ear infections or allergies to ear molds—you may need a bone-anchored hearing system. You might also consider a bone conduction hearing aid worn with a headband. Like TransEar, the device transmits sounds via vibration to the cochlea on the other side. 

Ideally you could fix the hearing in your bad ear. In 2019, the U.S. Food and Drug Administration approved the first cochlear implant for people with single-sided deafness. A March 2020 reviewcovering 20 studies concluded that for people with SSD, both cochlear implants and bone-anchored solutions were helpful. When adults and children took tests of their ability to identify speech against background noise without help, they answered only 15 percent of the questions correctly; cochlear implants boosted that score to 43 percent.

Cochlear implants also improved their ability to locate the source of a sound, and cut the perceived volume of tinnitus by more than half. Hearing-related quality of life more than doubled. 


You might try smart headphones with features that allow you to customize the sounds you amplify or suppress. For example, Bose Hearphones allow you to mute one side and amplify the other.

Iphones have a setting that gives you full stereo sound coming out of just one ear bud. 

Drawbacks to CROS hearing aids

CROS hearing aids take time to get used to, and it’s important to know they will not solve all the hearing problems a person may have. For example, they do not improve “localization” of sound—a person may still not know where a sound is originating from. This can be especially frustrating in an environment with a lot of background noise, which will be amplified by the devices.

What can I do to improve my chance of adjusting well?

While getting used to them can be challenging, the most important thing a person can do is wear their CROS aid as much as possible, experts say, and not give up too quickly. 

“Use the device full time—all waking hours—in order to get used to this listening arrangement. It is very different from what anyone is used to and it will take time to adjust,” Palmer notes. 

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