Dementia is not a single disease, but a general term for memory loss and other intellectual disabilities serious enough to interfere with daily life.

Alzheimer's disease is the most common cause of dementia, among many other causes, such as vascular dementia, which causes brain damage from cerebrovascular or cardiovascular problems, and HIV-associated dementia, or infection of the brain with HIV virus.

The mechanism of dementia is not clear, but dementia results from the death and damage of nerve cells in the brain.