Exactly what causes auditory processing disorder isn't fully understood. Sometimes a possible underlying factor is identified, but not always.
In children, the condition may occur after a persistent hearing problem at a young age, such as glue ear, which has since passed but has had a permanent effect on how the brain processes sound. It may also be caused by a genetic defect, as some cases seem to run in families.
In adults and children, the condition may be associated with damage to the brain from a head injury, stroke, brain tumour or meningitis.
Some cases in adults have also been linked to age-related changes in the ability of the brain to process sounds and progressive conditions affecting the nervous system, such as multiple sclerosis.