You can buy just one hearing aid, but we  do not recommend it. Here's why...

• Your brain receives separate signals from each of your ears. This is called bilateral, or two-sided hearing.
• Bilateral hearing helps you locate the source of a sound, it helps you hear softer sounds, and most importantly, it helps you separate speech signals (such as your dinner partner) from background noise (such as restaurant clatter).
• If you only listen with one ear, you lose all of these advantages, and that can create stress on your auditory system. You may find yourself straining to listen and getting tired sooner.
• Over a period of years, even worse things can happen. Some studies have shown that the ability of the unaided ear to understand words gradually decreases. In other words, use it or lose it! If the brain stops receiving signals from one ear, it loses the ability to decode those incoming signals.
•  Two aids are recommended for people whose hearing is symmetrical (the same and equal) in both ears. If you have a "bad" ear and a "good" ear, you may only need one hearing aid; it is important to discuss your particular situation with your audiologist.