Alzheimer’s disease is a progressive brain disorder that slowly destroys memory, thinking skills, and eventually the ability to carry out basic daily tasks. It is the most common cause of dementia, accounting for 60% to 80% of all dementia cases. An estimated 7.2 million Americans age 65 and older are living with Alzheimer’s in 2025, and it ranks as the seventh leading cause of death in the United States.
Alzheimer’s vs. Dementia
One of the most common points of confusion is the relationship between Alzheimer’s and dementia. Dementia is not a disease itself. It’s an umbrella term for a decline in memory, reasoning, or decision-making severe enough to interfere with everyday life. Alzheimer’s is a specific disease, and the most common one under that umbrella. Other types of dementia include vascular dementia, Lewy body dementia, and frontotemporal dementia, each with different underlying causes. When someone is diagnosed with “dementia,” the next step is usually figuring out which type.
What Happens in the Brain
Two abnormal proteins drive the damage in Alzheimer’s disease. The first is beta-amyloid, a naturally occurring protein fragment that, in Alzheimer’s, clumps together into sticky plaques between brain cells. A particular form called beta-amyloid 42 is considered especially toxic. These plaques disrupt how neurons communicate with each other.
The second protein is tau. Normally, tau helps maintain the internal transport system that moves nutrients and other essential materials through neurons. In Alzheimer’s, tau undergoes abnormal chemical changes, detaches from its structure, and clumps into tangles inside the neurons themselves. These tangles block the cell’s transport system, starving it of what it needs to function. Tau tangles tend to accumulate first in brain regions involved in memory, which is why memory loss is typically the earliest symptom.
Once beta-amyloid reaches a tipping point, tau spreads rapidly throughout the brain. As more neurons are damaged and die, the brain physically shrinks. This process begins years, sometimes decades, before any noticeable symptoms appear.
Stages and Symptoms
Alzheimer’s progresses through recognizable stages, though the pace varies widely from person to person. The full course from first symptoms to end of life typically spans 4 to 8 years but can stretch much longer.
Early Stage
The earliest changes are subtle. You might notice mild memory lapses, particularly with recently learned information or things that are usually easy to recall: an appointment, a name, where you put your keys. At this point, most people can still work, drive, and manage their daily lives independently. These changes are often dismissed as normal aging, which is why early-stage Alzheimer’s frequently goes undiagnosed.
Middle Stage
This is typically the longest stage and where changes become impossible to overlook. People may grow confused about where they are or what day it is. Personality shifts are common: restlessness, agitation (especially in the late afternoon and evening), suspicion of loved ones, or seeing and hearing things that aren’t there. Some individuals experience outbursts of aggressive behavior. Day-to-day tasks like cooking, managing finances, or choosing appropriate clothing become increasingly difficult, and more hands-on help is needed.
Late Stage
In severe Alzheimer’s, people lose the ability to communicate, recognize loved ones, or control movement. They become fully dependent on others for eating, bathing, and all personal care. The body’s basic functions gradually decline, and complications like infections become the most common immediate cause of death.
Risk Factors
Age is the single biggest risk factor. Most people with Alzheimer’s are 65 or older, and about 1 in 9 Americans in that age group has the disease. But Alzheimer’s is not a normal part of aging.
Genetics play a role too. One gene variant in particular, called APOE-e4, significantly raises risk. Carrying one copy of this variant doubles or triples your likelihood of developing Alzheimer’s. Carrying two copies makes you 8 to 12 times more likely. That said, many people with the variant never develop the disease, and many people without it do.
A landmark analysis by the Lancet Commission identified 14 modifiable risk factors spread across a person’s lifetime. In early life, low educational attainment increases risk. In midlife, the key factors are hearing loss, traumatic brain injury, high blood pressure, excessive alcohol use, and obesity. In later life, the list includes smoking, depression, social isolation, physical inactivity, diabetes, air pollution exposure, vision loss, and high LDL cholesterol. Addressing all 14 of these factors could potentially prevent roughly 45% of dementia cases worldwide. That number is striking because it means nearly half of all dementia risk is not fixed at birth.
Early-Onset Alzheimer’s
While Alzheimer’s overwhelmingly affects people over 65, a small number develop it much earlier. Early-onset (or young-onset) Alzheimer’s can appear in people in their 40s or 50s, and in rare cases even younger. It affects about 110 out of every 100,000 adults between ages 30 and 64. The symptoms are the same, but the impact on careers, finances, and family life can be especially disruptive at an age when the diagnosis is least expected. Early-onset cases are more likely to have a strong genetic component.
How Alzheimer’s Is Diagnosed
Diagnosis starts with cognitive testing and a detailed medical history, often gathered from both the patient and a family member who has observed the changes. But in recent years, the tools available have become much more precise. Brain imaging using PET scans can now detect amyloid plaques directly, using specialized tracers that bind to the protein deposits and make them visible. Three of these tracers are FDA-approved and in clinical use.
Spinal fluid testing offers another window into the brain’s biology. In Alzheimer’s, levels of beta-amyloid 42 in spinal fluid drop (because the protein is being trapped in plaques rather than flowing freely), while tau levels rise. This combination creates a biochemical signature that can confirm Alzheimer’s even in its early stages. Blood-based biomarker tests are also emerging as a less invasive option, though spinal fluid and PET imaging remain the most validated tools in specialized settings.
Treatment Options
For decades, the only available medications managed symptoms without addressing the underlying disease. That changed recently with the approval of a new class of drugs: monoclonal antibodies that target and clear amyloid plaques from the brain.
Lecanemab received full FDA approval in July 2023 and European approval in late 2024. Donanemab followed with FDA approval in July 2024 and European authorization in 2025. Both are given by infusion and are intended for people in the early stages of Alzheimer’s with confirmed amyloid buildup. In clinical trials, they consistently cleared amyloid from the brain and slowed cognitive decline, though the benefit was modest. An earlier drug called aducanumab was approved in 2021 but was discontinued by its manufacturer in 2024 after questions about its effectiveness.
These treatments are not cures. They slow progression rather than stop or reverse it, and they carry risks including brain swelling and small brain bleeds that require regular monitoring with MRI scans. Still, they represent the first therapies that actually alter the course of the disease rather than just managing symptoms.
The Outlook
Alzheimer’s remains a disease without a cure, and the number of people affected is growing. By 2060, the number of Americans 65 and older living with Alzheimer’s is projected to nearly double to 13.8 million. Globally, 68% of the increase in dementia cases by 2050 is expected to occur in low- and middle-income countries, where access to new treatments and diagnostic tools remains limited.
What has changed is the ability to detect the disease earlier and, for the first time, to intervene at a biological level. Combined with the evidence that nearly half of dementia risk is tied to factors people can actually modify, the picture is more nuanced than it was even five years ago. The disease is still devastating, but the tools to fight it are no longer limited to symptom management alone.