Alzheimer disease is a progressive neurological disorder that leads to the degeneration and death of brain cells. It 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. The disease primarily affects those aged 65 and older but can also present at an earlier age.

Alzheimer is categorized into different stages: mild (early stage), moderate (middle stage), and severe (late stage). The disease progression varies among individuals, but it generally intensifies in complexity and severity over time.