Alzheimer's Disease

The most common cause of dementia—what happens in the brain, symptoms, risk factors, diagnosis and today's treatments.

Last reviewed: October 2026

Alzheimer's disease is a progressive brain disease that slowly damages memory, thinking and, eventually, the ability to carry out everyday tasks. It is the most common cause of dementia, responsible for an estimated 60–80% of cases. It was first described in 1906 by the German doctor Alois Alzheimer.

What happens in the brain

Two abnormal proteins are the hallmarks of Alzheimer's:

Amyloid plaques – clumps of a protein fragment called beta-amyloid that build up between nerve cells.
Tau tangles – twisted strands of a protein called tau that build up inside nerve cells and disrupt their transport system.

Along with these, the brain's immune cells become chronically activated (inflammation), connections between nerve cells are lost, and brain tissue shrinks. Damage usually begins in the hippocampus and nearby areas involved in forming memories, which is why recent memory is typically affected first. Over time it spreads to areas for language, reasoning and behavior.

Remarkably, these changes begin 10 to 20 years before symptoms appear. This long silent phase is why researchers are focused on early detection and prevention.

Symptoms

Alzheimer's usually develops gradually. Early signs include:

Forgetting recently learned information, important dates or conversations
Asking the same questions repeatedly
Increasing reliance on notes or family for things once handled alone
Trouble planning, following a recipe, or keeping track of bills
Losing track of dates and seasons
Misplacing things and being unable to retrace steps
Word-finding problems and withdrawal from social activities
Changes in mood: anxiety, depression, irritability, suspicion

As the disease progresses, people need more help with daily activities, may not recognize family members, and may experience behavior changes such as wandering, agitation or Sundowning. In the late stage, people need full-time care. See Stages of Dementia and 10 Early Warning Signs of Alzheimer's and Dementia.

Some people have atypical forms in which the first symptoms are problems with vision and spatial skills (posterior cortical atrophy), language (logopenic aphasia), or planning and behavior.

Who gets it? Risk factors

Age – the biggest risk factor. Most people with Alzheimer's are 65 or older; risk roughly doubles every five years after 65. When it begins earlier it is called young-onset.
Genes – the APOE4 gene variant raises risk (one copy modestly, two copies substantially), but many people with APOE4 never develop Alzheimer's. Rare mutations in the APP, PSEN1 or PSEN2 genes cause inherited early-onset Alzheimer's.
Family history – having a parent or sibling with Alzheimer's increases risk.
Down syndrome – people with Down syndrome have a very high risk, because the APP gene is on chromosome 21.
Modifiable factors – high blood pressure, diabetes, physical inactivity, hearing loss, smoking, depression, social isolation and others. See Reducing Dementia Risk: The 14 Risk Factors.
Sex – nearly two-thirds of Americans with Alzheimer's are women, partly because women live longer; researchers are studying other reasons.

Diagnosis

There is no single test. Doctors combine a medical history, conversations with family, cognitive tests, a physical and neurological exam, and blood tests to rule out other causes. Brain scans (MRI or CT) look for strokes, tumors or other problems. To confirm Alzheimer's biology, doctors can now use amyloid PET scans, spinal fluid tests, and—increasingly—FDA-cleared blood tests that measure proteins such as p-tau217. A biomarker-confirmed diagnosis is required before starting anti-amyloid treatment. See Getting a Diagnosis.

Treatment

There is no cure yet, but there are treatment options:

Anti-amyloid antibodies – Lecanemab (Leqembi) (Leqembi) and Donanemab (Kisunla) (Kisunla) remove amyloid and modestly slow decline in people with mild cognitive impairment or mild dementia due to Alzheimer's. They require infusions and MRI monitoring because of a risk of brain swelling or bleeding (ARIA).
Symptom medicines – Cholinesterase Inhibitors and Memantine (donepezil, rivastigmine, galantamine) and memantine can help memory and thinking for a time in some people.
Non-drug approaches – exercise, social engagement, music, routine, and support for caregivers improve quality of life. See Non-Drug Treatments for Dementia.
Treating other conditions – managing blood pressure, hearing, vision, sleep, depression and pain can make a meaningful difference.

See Dementia Treatments: An Overview for more.

Outlook

Alzheimer's progresses at different rates in different people. On average, people live 4 to 8 years after diagnosis, but some live 20 years or more. Good care, planning and support make an enormous difference to quality of life for the person and their family.

Getting help

If you're worried about yourself or someone you love, talk to a doctor. For 24/7 support, call the Alzheimer's Association Helpline at 800-272-3900, or contact the NIA's ADEAR Center at 800-438-4380.

Free printable: 10 Warning Signs of Dementia: Checklist (large-print PDF) · Questions to Ask the Doctor (large-print PDF)

Sources

Not medical advice. This article is general information, not a diagnosis or treatment plan for any individual. Talk with a doctor about your situation.

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We may answer common questions in future updates (we won't share your name). We can't give personal medical advice; for urgent help call the Alzheimer's Association Helpline at 800-272-3900.

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