Defining dementia

Because brains have so many different roles, illnesses that harm the brain can have devastating effects.

Certain diseases affect a person’s brain gradually. Over several months or years, a person with one of these diseases may begin to have many different problems.

People living with dementia may start to have problems with remembering, thinking, concentrating or speaking. They may find it more difficult to do everyday things. Their behaviour or personality might begin to change, so they say or do things that seem strange. They may not seem like the same person they used to be. Some people may have difficulties with their vision because their brain is struggling to process what their eyes are seeing. Not everyone with dementia gets all of these problems and at first they may just have one or two of them.

We use the word dementia to describe these different symptoms. Dementia is a word that describes a collection of symptoms that can have different underlying causes. When a person has signs of dementia, doctors try to find out which disease is causing the problems.


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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.