Dementia: Facts about Alzheimer's and other forms of dementia

An illustration of a man's silouette, with the top half of the head fading as if into a fog.

Dementia is a group of diseases that involve having trouble with memory, thinking, reasoning and other brain functions. It is often associated with "neurodegeneration," meaning processes that destroy brain cells and get worse over time. Alzheimer's disease is the most common form of dementia, but there are other types.

Over 57 million people in the world currently have some form of dementia. People ages 65 and older are at higher risk for dementia than younger age groups, but the conditions can occur in younger people as well. As many as one-third of people 85 and older have some form of dementia, highlighting how the risk of the conditions rises with age, but not everyone develops them.