Dementia is an overall term for diseases and conditions characterized by a decline in memory, language, problem-solving and other thinking skills that affect a person's ability to perform everyday activities. Memory loss is an example. Alzheimer's is the most common cause of dementia. Not a specific disease, dementia is a group of conditions characterised by impairment of at least two brain functions, such as memory loss and judgment.

Alzheimer's disease is a progressive disorder that causes brain cells to waste away (degenerate) and die. Alzheimer's disease is the most common cause of dementia — a continuous decline in thinking, behavioral and social skills that disrupts a person's ability to function independently. Brain cell connections and the cells themselves degenerate and die, eventually destroying memory and other important mental functions.