2. Causes of aggressive behaviour

People with dementia have the same needs as everyone else, including comfort, social interaction, stimulation, emotional wellbeing and being free from pain. However, people with dementia may be unable to recognise their needs, know how to meet them, or communicate what they need to others. This may cause them to act in ways that others might find challenging, including aggression. The aggressive behaviour might be the person's way of meeting the need, an attempt to communicate it, or an outcome of the unmet need. For example, if a person with dementia is not getting enough stimulation they might become bored, and this may lead to them behaving in a way that others might find challenging, such as walking about or following their carer. Meeting the need by providing stimulation to the person may stop the behaviour as they will no longer be bored.

Understanding what is causing the person's behaviour can help carers to find a solution. Some possible explanations for aggression are listed below. The causes could be biological, social or psychological.


  • There may be pain, illness (including infections) or physical discomfort (including being constipated or thirsty, or from sitting for too long).
  • Side effects and/or taking too many medications may mean that a person becomes more confused and drowsy. This means they may be less able to problem-solve their way out of distressing situations.
  • The environment may not meet their needs or may be over-stimulating. It could be too hot or too cold, noisy or too bright. Poor eyesight or hearing can lead to misunderstandings and misperceptions.
  • Hallucinations (where people see things that aren't there) and/or delusions (where people believe things that aren't true) can be confusing and frightening, leading the person with dementia to respond to them in an aggressive way.
  • The physical effects of dementia may have affected the person's judgement and self-control. They may have lost their inhibitions or have a decreased awareness of what kind of behaviour is appropriate.


  • Lack of social contact and loneliness.
  • Boredom, inactivity and sensory deprivation.
  • Different carers coming in with a different approach or changing the established routine.
  • Not liking or trusting a particular carer.
  • Trying to hide their condition from others.


  • The person with dementia may have a perception that their rights are being infringed or that they are being ignored. This may be due to misperceptions, memory difficulties or problems processing information, but it may also be true.
  • The person may become frustrated at not being able to complete tasks, eg making a cup of tea.
  • There may be depression or other mental health problems.
  • A carer's intentions may be misunderstood. For example, personal care may be seen as threatening or an invasion of personal space. Accepting help with intimate tasks such as washing, dressing or going to the toilet is understandably distressing and stressful.
  • Others may assume that the person with dementia can no longer do things for themselves or leave them out of decisions that affect them. This can cause the person with dementia to become angry because they are not being listened to or are being ignored. The person may feel threatened by an environment that appears strange or unfamiliar. They may think that they are in the wrong place or that there are strangers in their home.
  • People may have difficulties understanding and interpreting the world around them, and may experience a different sense of reality from others. For example, if the person believes that they need to collect their children from school, they may become aggressive if they are prevented from doing so.