• Each individual has a unique hearing trajectory that is shaped by diverse
  influences experienced throughout the life course; these include genetic
  characteristics, and biological, behavioural and environmental factors.
•  The course of the hearing trajectory determines a person’s hearing capacity
  at any point during their life. Causative and protective factors influence
  hearing capacity.
• Although factors influencing hearing capacity can be encountered at
  different periods of a person’s life, some factors are more likely to be
  experienced – or individuals may be most susceptible to their effects – at
  specific points in life.
• Section 1 describes the causative and protective influences encountered
  during the prenatal period through to older age, with emphasis placed on
  those most relevant to public health.
• Hearing capacity is commonly measured using pure tone audiometry
  and classified based on the audiometric hearing thresholds. Any decline
  in hearing capacity is referred to as hearing loss or hearing impairment2
  which may range in severity from mild to complete.
• Globally more than 1.5 billion people experience some degree of hearing
  loss. Of these, an estimated 430 million have hearing loss of moderate or
  higher severity in the better hearing ear. Prevalence of hearing loss varies
  across WHO regions; the vast majority of people affected live in low- and
  middle-income countries of the world.
• The impact of hearing loss on a person is determined not only by the
  severity and profile of the loss, but also largely on whether the hearing
  loss is addressed by effective clinical or rehabilitative interventions, and
  the extent to which the environment is responsive to the person’s needs.
• If unaddressed, hearing loss can negatively impact many aspects of life:
  communication; the development of language and speech in children;
  cognition; education; employment; mental health; and interpersonal
  relationships. Hearing loss can cause low self-esteem, is often associated
  with stigma, and can significantly impact the families and communication
  partners of those living with the condition.
• Globally, unaddressed hearing loss poses an annual cost of over $ 980 billion.3
  This includes costs related to health care, education, productivity losses,
  and societal costs. Many of these costs can be mitigated through the use
  of cost–effective interventions, as described later in the report.
• Hearing is a key component of human intrinsic capacity; it is the sense most relied
  upon to communicate and engage with others. Any decline in hearing capacity at
  any point during the life course, if not addressed in a timely manner, can adversely
  affect day-to-day functioning (1, 2). Section 1 highlights these factors and explores
  the impact of unaddressed hearing loss on those affected, their families and society
  as a whole.