A person is said to have hearing loss if they are not able to hear as well as someone with normal hearing, meaning hearing thresholds of 20 dB or better in both ears. It can be mild, moderate, moderately severe, severe or profound, and can affect one or both ears. Major causes of hearing loss include congenital or early onset childhood hearing loss, chronic middle ear infections, noise-induced hearing loss, age-related hearing loss, and ototoxic drugs that damage the inner ear.

The impacts of hearing loss are broad and can be profound. They include a loss of the ability to communicate with others delayed language development in children, which can lead to social isolation, loneliness and frustration, particularly among older people with hearing loss. Many areas lack sufficient accommodations for hearing loss, which effect academic performance and options for employment. Children with hearing loss and deafness in developing countries rarely receive any schooling. WHO estimates that unaddressed hearing loss costs the global economy US$ 750 billion annually due to health sector costs (excluding the cost of hearing devices), costs of educational support, loss of productivity and societal costs.