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What is Alzheimer’s disease?


Dementia is the name for a set of symptoms that includes memory loss and difficulties with thinking, problem-solving or language. Dementia develops when the brain is damaged by diseases, including Alzheimer’s disease. Alzheimer’s disease is a physical disease that affects the brain. It is named after Alois Alzheimer, the doctor who first described it.

The brain is made up of billions of nerve cells that connect to each other. In Alzheimer’s disease, connections between these cells are lost. This is because proteins build up and form abnormal structures called ‘plaques’ and ‘tangles’. Eventually nerve cells die and brain tissue is lost.

The brain also contains important chemicals that help to send signals between cells. People with Alzheimer’s have less of some of these ‘chemical messengers’ in their brain, so the signals are not passed on as well. There are some drug treatments for Alzheimer’s disease that can help boost the levels of some chemical messengers in the brain. This can help with some of the symptoms.

Alzheimer’s is a progressive disease. This means that gradually, over time, more parts of the brain are damaged. As this happens, more symptoms develop, and they also get worse.


The symptoms of Alzheimer’s disease are generally mild to start with, but as more brain cells are damaged over time the symptoms get worse and start to interfere with a person’s day-to-day life. This makes them different from the changes that lots of people have as they get older, such as being a bit slower at thinking things through or forgetting something occasionally.

There are some common symptoms of Alzheimer’s disease, but no one’s experience will be exactly the same as anyone else’s.

For most people, the first signs of Alzheimer’s are problems with their memory – in particular, difficulties recalling recent events and learning new information. This is because early on in Alzheimer’s the damage is usually to a part of the brain called the hippocampus. This has a big role in day-to-day memory. However, the person’s memory for events that happened a long time ago is not usually affected in the early stages.

As Alzheimer’s disease progresses, memory problems will usually affect someone’s daily life more and they may:

lose items (such as keys and glasses) around the house
forget a friend’s name, or struggle to find the right word in a conversation and forget about recent conversations or events
they may get lost in a familiar place or on a familiar journey
forget appointments or significant dates.

As well as memory difficulties, people with Alzheimer’s are also likely to have – or go on to develop – other problems. These include problems with thinking, reasoning, language or perception such as:

speech – they may repeat themselves or struggle to follow a conversation

seeing things in three dimensions and judging distances (visuospatial skills) – going up or down stairs or parking the car might become much harder

concentrating, planning or organising – they may struggle with making decisions, solving problems or carrying out a sequence of tasks (such as cooking a meal)

orientation – they may become confused or lose track of the day or date.

A person in the earlier stages of Alzheimer’s will often have changes in their mood. They may become anxious, depressed or more easily annoyed. Many people lose interest in talking to people, or in activities and hobbies. These changes can be challenging for both the person with dementia and those close to them to live with. Anyone finding things difficult should ask for support from a GP or other professional.


Later stages

As Alzheimer’s progresses, problems with memory loss, language, reasoning and orientation get much worse. A person with Alzheimer’s disease will need more day-to-day support.

Some people start to believe things that are untrue (having delusions) – for example, being convinced that someone is stealing from them. Less often, people see or hear things that are not really there (having hallucinations).

There are some common symptoms of Alzheimer’s disease, but no one’s experience will be exactly the same as anyone else’s.

Many people with Alzheimer’s also start to behave in ways that aren’t normal for them. These might include becoming agitated (for example, being very restless or pacing up and down), calling out, repeating the same question, having disturbed sleep patterns or reacting aggressively. This can be distressing and challenging both for the person and anyone caring for them. The person may need treatment and support for these behaviours which is separate from any treatment specifically for memory problems.

In the later stages of Alzheimer’s disease someone may become much less aware of what is happening around them. They may have difficulties eating or walking without help, and become more and more frail. Eventually, the person will need help with all of their daily activities.

How quickly the disease progresses, and the life expectancy of someone with Alzheimer’s, vary from person to person. On average, people with Alzheimer’s disease live for 8–10 years after the first symptoms. However, this varies a lot, depending especially on how old the person was when they first developed Alzheimer’s.

Around 1 in 10 people with dementia have more than one type at the same time.
This is called mixed dementia. The most common form of mixed dementia is Alzheimer’s disease with vascular dementia (caused by problems with the blood supply to the brain). The symptoms of this kind
of mixed dementia are a mixture of the symptoms of Alzheimer’s disease and vascular dementia. 

Atypical Alzheimer’s disease

In some people with Alzheimer’s disease, memory problems are not the first symptoms. This is called atypical Alzheimer’s disease. It is still caused by plaques and tangles, but the first part of the brain to be affected is not the hippocampus.

Atypical Alzheimer’s disease is not common in people diagnosed when they are over 65. Only around 1 in 20 people over 65 with Alzheimer’s disease have this atypical type. However, it’s more common in people diagnosed when they are under 65 to have early-onset Alzheimer’s disease

The atypical forms of Alzheimer’s disease are:

Posterior cortical atrophy (PCA) – this develops when there is damage to areas at the back of the brain. These areas process signals from a person’s eyes and help with spatial awareness. This means the early symptoms of PCA are often problems identifying objects or reading, even if the person’s eyes are healthy. Someone may also struggle to judge distances when going down stairs, or seem uncoordinated (for example when they’re getting dressed).

Logopenic aphasia – this develops when there is damage to the areas in the left side of the brain that produce speech. The person may have problems finding the right word, or take long pauses while they’re speaking.


Frontal variant Alzheimer’s disease – this develops when there is damage to the lobes at the front of the brain. The symptoms include problems with planning and decision-making. The person may also behave in socially inappropriate ways (such as saying things that other people might find rude) or seem not to care about the feelin

Who gets Alzheimer’s disease?

Most people with Alzheimer’s disease develop it after the age of 65, but people under this age can also develop it. This is called early-onset Alzheimer’s disease, a type of young-onset dementia. In the UK there are over 40,000 people under the age of 65 with dementia. For more information see factsheet 440, What is young-onset dementia?.


There are many different factors that affect whether someone gets Alzheimer’s disease. Some of these risk factors can be changed, but others cannot. For more information see factsheet 450, Risk factors for dementia, or booklet 35, Dementia: Reducing your risk.

Risk factors you can’t change



Age is the biggest risk factor for Alzheimer’s. It mainly affects people
over 65. Above this age, a person’s risk of developing Alzheimer’s disease doubles about every five years. One in six people over 80 have dementia – many of them have Alzheimer’s disease.

Please see this factsheet for more information:

* This list is not comprehensive - We have included information here

on the most common types of dementia

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