4 things you should know about UHL and CROS

Audiologists Jane Woodward and Dr. Elizabeth Stewart reviewed 10 years’ worth of UHL and CROS literature. Here are 4 lightbulb moments from their review.

Recently a friend got in contact as she had a sudden unilateral hearing loss (UHL). Out of nowhere, she was unable to hear in her right ear, struggled to hear conversations while out in noisy surroundings and was disturbed by tinnitus. She worried that the hearing in her left ear might drop as well.

My heart went out to her and my immediate thought was, ‘how can I help? I have been lucky enough to be part of the team at Phonak developing our CROS P solution for UHL and became curious.

How common is UHL? What will help combat some of these challenges?

Working with research audiologist, Dr. Elizabeth Stewart, we reviewed 10 years’ worth of CROS and UHL literature. This literature review changed how I think about UHL and I want to share some of our lightbulb moments.

4 things you should know about UHL and CROS systems

  1. UHL is more common than you might think.

UHL is any degree of hearing loss in one ear with normal hearing on the other side.1

  • Around 1 in 1000 newborns in the US are identified at birth with UHL.2  This number increases to approximately 3 in 100 children who develop UHL by school age.3

  • The overall prevalence of unilateral hearing loss in American adults is estimated to be 7.2%, with 5.2% having a mild, and 1.5% a moderate or worse unilateral hearing loss.4  

That’s a lot of people. Working at my local ENT clinic in a town of 14,000 people in Switzerland, I supported six clients with UHL. Anecdotal but telling.

2. UHL is not half the problem of bilateral hearing loss.

Far from it. In fact, one recent study showed that difficulties following conversations in noise and the presence of tinnitus were significantly more likely with UHL compared to bilateral hearing loss.5

Alongside hearing challenges – reduced awareness of sounds, difficulties hearing in background noise or at a distance and localizing sounds – UHL is also associated with reduced well-being, decreased quality of life and increased loneliness.6,7

Carly Sygrove 8 summarized her experiences beautifully in her honest account for the British Academy of Audiology:

“Not only was I struggling to deal with the practical challenges of living with a reduced sense of hearing, but I was also overwhelmed by the emotional aspects of hearing loss such as feelings of isolation and the need to grieve the sound I had lost.”

3. CROS systems are evidence-based technical solutions specific for UHL.

CROS and BiCROS systems are non-surgical solutions for people who have one ear with no usable hearing; that means one ear for which conventional amplification provides no benefit, and either normal or aidable hearing in the other ear.  This is known as unaidable UHL, or single-sided deafness (SSD). 

  • In a CROS system, a microphone worn on the unaidable ear picks up sounds and transmits them wirelessly to a hearing aid worn on the ear with normal hearing.
  • A CROS system can also be configured as a BiCROS for clients who also have a hearing loss in their better hearing ear.

A number of independent studies showed improved speech understanding in noise when the speech is presented to the unaidable side, and the noise is on the normal hearing or aidable side.9-12

Additionally, there was further evidence of improved speech understanding in diffuse noise,13, 14  which is a more realistic listening environment and one of the challenges that my friend specifically mentioned.

There were other more subjective benefits too, like improvements in ease of communication and subjective sound quality.9, 11

4. Counseling is important to get the best out of CROS technology.

While CROS has considerable benefits, it cannot replace binaural hearing. Counseling is helpful to get the best out of CROS systems.

Things to keep in mind when counseling clients:

  • The literature showed that there is generally no improvement in localization with CROS as binaural hearing is not restored.14,15 It would be best to advise your clients to stay vigilant when in situations that might compromise safety (e.g., crossing a busy road).
  • CROS doesn’t help when noise is on the unaidable side, as the noise that was previously unheard on this side is passed over to the hearing ear.1,10-14 This should not be a huge problem, as we typically experience diffuse noise in real-life situations but it would be good to tell your clients to avoid noise on their unaidable side. If there is noise on the CROS side, such as a noisy fan, or when in a car, it might be best to mute the CROS.

So overall…

UHL is relatively common, and there are very real challenges for clients, like my friend, who we see in clinical practice. For those with unaidable UHL, the literature review has shown that there are evidence-based technology solutions available and also tools to fit these well.

With a wealth of literature behind us and a wonderful new product, I feel armed to help support those with UHL.

Special thanks to Dr Elizabeth Stewart for jointly carrying out the literature review and to David Crowhen for the informative CROS P verification guide. Find out about our latest Phonak CROS P solution which stands out from our previous platform with many proven Paradise features, rechargeability and universal connectivity.

For more information on UHL and CROS, I invite you to read the full literature review and listen to our recent Phonak podcast on CROS and UHL.


  1. Bagatto, M., DesGeorges, J., King, A., Kitterick, P., Laurnagaray, D., Lewis, D., Roush, P., Sladen, D. P., & Tharpe, A. M. (2019). Consensus practice parameter: audiological assessment and management of unilateral hearing loss in children. International Journal of Audiology. 58 (12), 805-815.
  2. Prieve, B., Dalzell, L., Berg, A., Bradley, M., Cacace, A., Campbell, D., DeCristofaro, J., Gravel, J., Greenberg, E., Gross, S., Orlando, M., Pinheiro, J., Regan, J., Spivak, L., and Stevens, F. (2000).The New York State universal newborn hearing screening demonstration project: Outpatient outcome measures. Ear and Hearing, 21 (2), 118-30.
  3. Bess, F.H., Dodd-Murphy, J. & Parker, R.A. (1998). Children with minimal sensorineural hearing loss: Prevalence, educational performance, and functional status. Ear and Hearing, 9, 339–354.
  4. Golub, J., Lin, F., Lustig, L., & Lalwani, A. (2018). Prevalence of adult unilateral hearing loss and hearing aid use in the United States. The Laryngoscope. 128 (7), 1681-1686.
  5. Pierzycki, R., Edmondson-Jones, M., Dawes, P., Munro, K. J., Moore, D. R., & Kitterick, P. T. (2020). Associations Between Hearing Health and Well-Being in Unilateral Hearing Impairment. Ear and Hearing. 42 (3), 520-530.
  6. Lucas, L., Roulla, K. & Kitterick, P.D. (2017). The psychological and social consequences of single-sided deafness in adulthood. International Journal of Audiology. 57 (1), 21-30.
  7. Wie O.B., Pripp A.H., Tvete O. (2010). Unilateral deafness in adults: effects on communication and social interaction. Ann Otol Rhinol Laryngol. 119 (11), 772-81.
  8. Sygrove, C. (2021). Take sudden hearing loss seriously! British Academy of Audiology (BAA) Magazine. Spring 2021, p29.
  9. Oeding, K., & Valente, M. (2013). Sentence recognition in noise and perceived benefit of noise reduction on the receiver and transmitter sides of a BiCROS hearing aid. J Am Acad Audiol, 24 (10), 980-991.
  10. Choi, J.E., Ma, S.M., Park, H., Cho, Y.S., Hong, S.H., & Moon, I. J. (2019). A comparison between wireless CROS/BiCROS and soft-band BAHA for patients with unilateral hearing loss. PLOS One, 14 (2), 1-17.
  11. Fogels, J., Jonsson, R., Sadeghi, A., Flynn, M., & Flynn, T. (2020). Single-Sided Deafness-Outcomes of Three Interventions for Profound Unilateral Sensorineural Hearing Loss: A Randomized Clinical Trial. Otol Neurotol, 41 (6), 736-744.
  12. Kuk, F., Seper, E., Lau, C., Crose, B., & Korhonen, P. (2015). Effects of Training on the Use of a Manual Microphone Shutoff on a BiCROS Device. J Am Acad Audiol, 26 (5), 478-493.
  13. Dwyer, R. T., Kessler, D., Butera, I. M., & Gifford, R. H. (2019). Contralateral Routing of Signal Yields Significant Speech in Noise Benefit for Unilateral Cochlear Implant Recipients. J Am Acad Audiol, 30 (3), 235-242.
  14. Picou, E. M., Davis, H., Lewis, D., & Tharpe, A. M. (2020). Contralateral Routing of Signal Systems Can Improve Speech Recognition and Comprehension in Dynamic Classrooms. J Speech Lang Hear Res, 63 (7), 2468-2482.
  15. Snapp H. A., Holt F. D., Liu X., Rajguru S.M. (2017). Comparison of Speech‐in‐Noise and Localization Benefits in Unilateral Hearing Loss Subjects Using Contralateral Routing of Signal Hearing Aids or Bone‐Anchored Implants. Otol Neurotol. 38 (1), 11‐18.