One or two hearing aids?
If you have a bilateral hearing loss (a hearing loss in both ears) it is generally recommended that you use two hearing aids. With two hearing aids, you will hear better and be more able to localise sounds. If you only use one hearing aid, you will more or less only hear with one ear and one side of your head, making it difficult to hear well in many situations.
Today, most people who have a bilateral hearing loss therefore use two hearing aids. People who use two hearing aids use their hearing aids more and report much better hearing and greater user satisfaction than those who use only one hearing aid.
Unilateral hearing loss
But if you have a unilateral hearing loss (hearing loss in one ear) you typically only need a hearing aid in the affected ear.
In some special cases of unilateral hearing loss where there is no hearing or practically no hearing left, a special type of hearing aid called a CROS hearing aid is often used. A CROS hearing aid sends the sound from the affected ear to the normal hearing ear. Another possibility in this case is to use a hearing implant such as a cochlear implant or a bone conduction device.