Is dementia the same as Alzheimer's?
No. Dementia is an umbrella term for symptoms like memory loss and confusion that interfere with daily life. Alzheimer's is a specific brain disease, and the most common cause of dementia, behind an estimated 60 to 80 percent of cases. All Alzheimer's is dementia, but not all dementia is Alzheimer's.
People use "dementia" and "Alzheimer's" as if they mean the same thing. They are related, but they are not interchangeable, and the difference actually helps.
Dementia is the symptoms, Alzheimer's is a cause
Think of dementia as the "what" and Alzheimer's as one of the "whys." As the Alzheimer's Association puts it, dementia is a general term for a decline in memory and thinking severe enough to interfere with daily life. Alzheimer's disease is a specific illness, a physical disease of the brain, that produces those symptoms.
So the relationship is one-directional: Alzheimer's causes dementia, but dementia has other causes too. All Alzheimer's is dementia; not all dementia is Alzheimer's.
How common is Alzheimer's?
Very. It is the most common cause of dementia by a wide margin, behind an estimated 60 to 80 percent of cases. That is why the two words get blurred together. But the remaining share matters: vascular dementia, Lewy body dementia, and frontotemporal dementia are all real and reasonably common, and each behaves differently.
Why the distinction is useful
Knowing the specific cause changes what to expect and how to help. Alzheimer's typically starts with memory, because it first affects brain regions involved in learning. Other types can start with movement, behavior, language, or judgment instead. A diagnosis of "dementia" is a starting point; the more useful answer is which disease is causing it, which a doctor works out through history, cognitive tests, and sometimes scans.
If someone has been told they have dementia, it is worth asking the doctor which type, and what that means for the road ahead.
This is general information, not medical advice. Every situation is different, so talk to a doctor about yours.