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 symptoms. For some people, the first signs of dementia may be forgetfulness or confusion. For others, it may be changes in their behaviour and mood, or problems with speaking or seeing things around them.

As time goes on, the diseases that cause dementia start to affect more of a person’s brain and cause new problems and symptoms. It is also possible to have more than one type of dementia at the same time, this is called mixed dementia and means people can have a mixture of different symptoms.

By understanding the diseases 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 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, causing symptoms like memory loss. Researchers are working hard to understand what causes a person’s brain to start changing in this way.

Common symptoms can include:


Regularly forgetting recent events, names and faces.


Uncertainty about the time of day.


Disorientation, especially away from normal surroundings. Getting lost.


Problems finding the right words.

Mood and behaviour

Some people become disinterested in what’s happening around them, become anxious or irritable, or lose confidence.


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. This damages the brain cells which can 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.

Common symptoms can include:

Thinking skills

Becoming slower in thinking.

Personality changes

These may include depression and apathy (becoming disinterested in things). People may also become more emotional.

Movement problems

Difficulty walking or changes in the way a person walks.

Dementia with Lewy bodies

Dementia with Lewy bodies, also called 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 and stiff arm and leg movements and changes with sleep, like talking or moving about during 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.

Some of the ways people are affected:


Changes in alertness, attention, and confusion, which may be unpredictable and change from hour to hour or day to day.

Movement problems

Parkinson’s disease-type symptoms such as slowed movements, muscle stiffness and tremors.

Visual hallucinations

These can involve seeing people or animals that aren’t really there.


Sleep disturbances which can cause people to move or talk in their sleep.


Unsteadiness and falls.

Frontotemporal dementia

Frontotemporal dementia, also called FTD, is caused by damage to the front and side 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 front and side 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 young-onset dementia, which is the name for people who have dementia under the age of 65 years old.


Below are some of the common symptoms of FTD:

Personality changes

A can change in how people express their feelings, or it might be a lack of understanding of other people’s feelings. They may also show a lack of interest or not be worried about things that used to worry them, people can start to behave inappropriately.

Communcation problems

Some people can't understand the meaning of words, or struggle to have a conversation with others. This is called aphasia.

Lack of personal awareness

People may fail to maintain their normal level of personal hygiene and appearance.

Lack of social awareness

This might include making inappropriate jokes or being rude to someone.


Changes in foods they like, for example developing a sweet tooth. People might start to over-eat or drink too much.

Behaviour changes

People may have a change their sense of humour, or develop unusual beliefs, interests or obsessions. Some people become impulsive or easily distracted.

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This information was updated in November 2021 and is due for review in November 2023. Please contact us if you would like a version with references.