Delirium vs Dementia: What is the Difference?

Delirium and dementia are both conditions that affect memory, thinking, and behaviour, but they are not the same thing. Confusing the two is common, particularly in older people. Understanding the difference is important because delirium is often reversible, while dementia is usually progressive.

This guide explains the key differences between delirium and dementia, how to recognise the signs, and when to seek medical help.

What Is Delirium?

Delirium is a sudden change in mental state that develops over hours or days. It often causes confusion, disorientation, and changes in attention or awareness.

The NHS describes delirium as a serious medical condition that requires urgent assessment, particularly in older people, as it is often caused by an underlying illness or infection and may be reversible if treated quickly:

Delirium is usually triggered by a medical issue and should always be taken seriously.

Common symptoms of delirium

• Sudden confusion or disorientation
• Difficulty concentrating or following conversations
• Rapid changes in alertness (drowsy one moment, agitated the next)
• Hallucinations or paranoia
• Disturbed sleep–wake cycle
• Sudden changes in behaviour or mood

Symptoms often fluctuate throughout the day, which is a key feature of delirium.

What Is Dementia?

Dementia is a long-term condition caused by progressive damage to the brain. It develops gradually over months or years and affects memory, thinking, communication, and daily functioning.

According to the NHS, dementia affects memory, thinking, and the ability to carry out everyday activities:

Unlike delirium, dementia is not caused by a single illness and cannot usually be reversed, although symptoms can sometimes be managed.

Can Someone Have Delirium and Dementia?

Yes. Delirium can occur in someone who already has dementia, and this is very common, particularly during hospital stays or illness.

People with dementia are at higher risk of delirium, and when delirium develops, symptoms of dementia can suddenly appear much worse.

Age UK highlights delirium as a condition that is often missed in older people, particularly those living with dementia, and stresses that sudden confusion should always be medically assessed.

What Causes Delirium in Older People?

Delirium often has a clear trigger. Common causes identified by the NHS and Age UK include:

• Infections, especially urinary tract infections (UTIs), are a common cause of sudden confusion in older people
• Dehydration or malnutrition
• Medication changes or side effects
• Pain
• Surgery or hospital admission
• Constipation or urinary retention

Treating the underlying cause is essential to recovery.

Why Delirium Is Often Missed

Delirium is sometimes mistaken for:

• Dementia
• Depression
• Normal ageing

This is particularly true if symptoms are mild or if the person already has memory problems. However, any sudden change in mental state should be treated as a medical concern.

When to Seek Medical Help

You should seek urgent medical advice if an older person:

• Becomes suddenly confused
• Shows rapid changes in behaviour or alertness
• Appears unusually drowsy or agitated
• Develops hallucinations

Early treatment of delirium can significantly improve outcomes.

Supporting Someone With Delirium or Dementia

Support focuses on reassurance, familiarity, and safety.

Helpful approaches include:

• Keeping surroundings calm and familiar
• Ensuring glasses and hearing aids are used
• Encouraging hydration and nutrition
• Providing gentle orientation
• Avoiding unnecessary changes to routine

Professional care at home can help monitor symptoms and reduce distress, particularly after hospital discharge, when the risk of delirium is higher. Elder explains how additional support after leaving hospital can reduce complications and readmission risk.

For people who need continuous reassurance or supervision during recovery, live-in care can provide one-to-one support at home, helping to manage confusion safely and reduce distress caused by unfamiliar environments.

Elder also offers specialist dementia care at home, supporting people to remain safe in familiar surroundings.

Why Understanding the Difference Matters

Recognising delirium vs dementia can:

• Prevent missed medical emergencies
• Reduce unnecessary distress
• Improve recovery and outcomes
• Help families advocate for the right care

While dementia develops slowly, delirium is often a warning sign that something is wrong and needs prompt medical attention.