Alzheimer's is the most common form of dementia, a general term for memory loss and other cognitive abilities serious enough to interfere with daily life. Alzheimer's disease accounts for 60 to 80 percent of dementia cases. The risk factor is increasing age, and the majority of people with Alzheimer's are 65 and older. The mechanisms behind Alzheimer’s disease aren’t well understood and there is competing for a hypothesis, but the most distinguishing feature of Alzheimer’s disease is the buildup of amyloid plaques and tau tangles in the brain. It’s widely believed that these brain changes are behind the disease. Alzheimer's disease is a progressive brain disorder that damages and eventually destroys brain cells, leading to memory loss and changes in thinking and other brain functions. It usually develops slowly and gradually gets worse as brain function declines and brain cells eventually wither and die. Many dementias are progressive, meaning symptoms start out slowly and gradually get worse. Symptoms vary and the disease progresses at a different pace according to the individual and the areas of the brain affected.