Causes of dementia

Many different illnesses can damage a person's brain and cause dementia, but some are much more common than others.

The chart below shows you the four main types of dementia and which are the most common.

Different types of dementia can affect different parts of the brain at first, and have their own pattern of signs and symptoms. For some people, the first signs of dementia may be forgetfulness or confusion. For others, it may be changes in behaviour and mood, or problems with speaking or seeing what and where things are.

As time goes on, the illnesses that cause dementia affect more of a person’s brain and cause new problems. It is also possible to have more than one type of dementia at the same time.

By understanding the illnesses that cause dementia, scientists hope to find ways to prevent, treat and even cure dementia in the future. You can find out more about dementia research by exploring our dementia research section.

Alzheimer’s disease

Alzheimer’s disease causes more than half of all cases of dementia. When people have this disease, the structure and chemistry of their brain begins to change. Sticky lumps of protein build up inside and around brain cells. This harms brain cells, and causes them to die. We don’t yet fully understand what causes a person’s brain to start changing in this way.

Vascular dementia

Vascular dementia is the second most common type of dementia. It is caused when blood vessels in the brain are damaged, meaning that less blood reaches the brain than normal. The damage may happen gradually over time, or suddenly, when a person has a stroke. In both cases, brain cells are damaged because they don’t get the oxygen and nutrients they need.

Dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the third most common cause of dementia.

Lewy bodies are tiny, round clumps of protein that build up inside brain cells. They stop brain cells from working properly, causing dementia symptoms such as memory loss. They can cause other problems too, such as hallucinations (seeing things that aren’t really there), slowed stiff movements and changes with sleep, causing people to talk or move about in their sleep.

People with DLB often have big differences between their good days and bad days. On bad days, they may be much more confused and less alert.

Frontotemporal dementia

Frontotemporal dementia (FTD) is caused by damage to the frontal and temporal lobes of the brain. These are the parts of the brain that control personality, emotions, behaviour, thinking and language. The symptoms of FTD can vary, depending on which parts of the frontal and temporal lobes are most affected. Although frontotemporal dementia is rare compared to Alzheimer’s disease and vascular dementia, it is the second most common cause of early-onset dementia, which is the name for dementia in people younger than 65 years old.


This information was updated in November 2019 and is due for review in November 2021. Please contact us if you would like a version with references.