Dementia vs. Alzheimer’s: Which Is It?

How to understand the difference — and why it matters

Kathleen Fifield and Cori Vanchieri,

Updated January 16, 2026

AARP

Reviewed by

Orly Avitzur, M.D.

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Published June 15, 2020

/ Updated January 16, 2026

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The terms “dementia” and “Alzheimer’s” have been around for more than a century, which means people have likely been mixing them up for that long too. But knowing the difference is important.

In the simplest terms, one is broader than the other. If the two were nesting dolls, Alzheimer’s would fit inside dementia, but not the other way around. While Alzheimer’s disease is the most common form of dementia, accounting for an estimated 60 to 80 percent of cases, there are several other types.

The second most common form is vascular dementia, which is caused by decreased blood flow to the brain and damage to blood vessels in the brain. Other types of dementia include Lewy body dementia and frontotemporal dementia. Some people may experience symptoms from more than one cause, a disorder known as mixed dementia. In addition, certain medical conditions and even medications can cause serious memory problems that resemble dementia.

A correct diagnosis is needed for people to get the right treatment, remedies and support. It is also a prerequisite for participating in a clinical trial of a new treatment.

What it is

Dementia

Simply put, dementia is a decline in mental function — thinking, remembering and reasoning — that is usually irreversible. It’s a syndrome, not a disease, notes neurologist Dr. Ronald Petersen, director of the Mayo Clinic Alzheimer’s Disease Research Center and the Mayo Clinic Study of Aging in Rochester, Minnesota.

Dementia encompasses several disorders that cause chronic memory loss, personality changes or impaired reasoning, Alzheimer’s disease being just one of them, says Dr. Daniel G. Blazer, a psychiatrist and professor emeritus at Duke University School of Medicine.

To be called dementia, the disorder must be severe enough to interfere with your daily life, says Dr. Constantine George Lyketsos, a psychiatrist and director of the Johns Hopkins Memory and Alzheimer’s Treatment Center in Baltimore.

What it’s not: Typical, mild forgetfulness that sometimes accompanies aging — say, having trouble remembering the name of an acquaintance who comes up to you on the street.

In fact, the earliest stage of dementia, known as mild cognitive impairment (MCI), is considered “forgetfulness beyond what is expected from aging,” Petersen says. With MCI, a person is still functioning normally — paying bills, driving well enough, doing their taxes — though performing some of those tasks may take longer than they used to. When someone starts to need regular assistance to do such daily activities, “that gets into the dementia range,” Petersen says. In fact, difficulty managing money can be a sign of declining brain health.

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Alzheimer’s disease

Alzheimer’s is a specific brain disease that progressively and irreversibly destroys memory and thinking skills. Age is the biggest risk factor for the disease. Eventually, Alzheimer’s disease takes away the ability to carry out even the simplest tasks.

Alzheimer's Facts

Alzheimer’s disease is the most common form of dementia, afflicting an estimated 7.2 million Americans older than 65, according to the Alzheimer’s Association. The disease is marked by progressive memory loss, personality changes and ultimately the inability to perform routine daily tasks, such as bathing, dressing and paying bills.

Alzheimer’s disease appears to involve an abnormal buildup of two proteins in the brain: beta-amyloid and tau, which hinder communications between nerve cells.

While a cure for Alzheimer’s remains elusive, researchers have made some progress developing treatments that may be able to slow the progression of the disease. The U.S. Food and Drug Administration has approved two drugs, Leqembi and Kisunla, for people with early-stage disease.

How it’s diagnosed

Dementia

A doctor must find that you have two cognitive or behavioral areas in decline to diagnose dementia. These areas are disorientation, disorganization, language impairment, mood change, personality change and memory loss.

Thanks to growing medical consensus that irritability, depression and anxiety often flag dementia before memory issues do, doctors are asking more about changes in mood or personality, Lyketsos notes.

To make an evaluation, a doctor (often a specialist such as a neurologist, psychiatrist or geriatric medicine physician) typically takes a patient history and administers several mental-skill challenges. Blood and urine tests are often done to identify reversible causes of the problem, such as urinary tract infections or a vitamin deficiency.

To check for cognitive decline, a doctor will ask whether a patient is experiencing just forgetfulness or is also having trouble figuring out calculations such as a restaurant tip, which is potentially more indicative of dementia, Petersen says. A physical exam can be important for flagging specific types of dementia caused by vascular disease (strokes) or Parkinson’s disease.

Next, a standard and fairly brief round of memory and thinking tests is given in the same office visit. Commonly used tests are the Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Mini-Cog. These tests may have the person draw a clock, recall terms or do some math.

Alzheimer’s

Doctors use several methods to determine if an individual has Alzheimer’s disease, according to the National Institute on Aging. Physical and mental evaluations are often part of this process. Memory and problem-solving tests are also used.

Before the early 2000s, a conclusive Alzheimer’s diagnosis was not possible until an autopsy was performed and the brain examined for the physical hallmarks of the disease — beta-amyloid and tau, the proteins that look like plaques and tangles in the brain.

Today, more diagnostic options exist. A patient can get a PET scan or cerebrospinal fluid sampling that can show, with high accuracy, whether plaques or tangles are present. The PET scan also measures glucose metabolism in the brain.

And two blood tests for Alzheimer’s disease were approved by the U.S. Food and Drug Administration in 2025. The tests are meant only for adults who are experiencing symptoms; they are not screening tests, according to the FDA.

Treatment options

There is no cure yet for Alzheimer’s disease. Medications may help with some symptoms, and two drugs may be prescribed for people with early-stage disease to slow the progression. Lifestyle changes have been shown to help slow disease progression in people diagnosed with mild cognitive impairment. Lifestyle changes have also made a difference for people who are at increased risk for dementia.

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Kathleen Fifield is a former AARP health editor who is now a senior writer at UNICEF USA.

Cori Vanchieri is executive editor for brain health at AARP.

Orly Avitzur, M.D., a former president of the American Academy of Neurology, is a practicing neurologist in Tarrytown, New York, and is working on a medical memoir, A Very Good Brain. She is a former medical director at Consumer Reports and a past editor in chief of Brain & Life magazine.