Disorders of consciousness can occur if the parts of the brain responsible for consciousness are injured or damaged.

The main causes can generally be divided into:

• traumatic brain injury
• non-traumatic brain injury
• progressive brain damage

Traumatic brain injury occurs when an object or outside force causes severe trauma to the brain.

This is most often caused by:

• falls
• traffic accidents
• violent assault

Find out more about head injury

Non-traumatic brain damage is usually caused by a health condition, such as:

• a condition that deprives the brain of oxygen (without a continuous supply of oxygen, brain tissue begins to die)
• a condition that directly attacks brain tissue

Specific causes of non-traumatic brain injury include:

• strokes
• heart attacks
• severe brain infections (such as meningitis, an infection of the outer layer of the brain, or encephalitis, an infection of the brain itself)
• drug overdoses
• poisoning
• almost drowning or other types of suffocation, such as smoke inhalation
• a blood vessel bursting, leading to bleeding inside the brain (the medical term for this is a ruptured brain aneurysm)

In some cases, brain damage can gradually occur over time.

Examples of conditions that cause progressive brain damage include:

• Alzheimer's disease
• Parkinson's disease
• a brain tumour