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

Common examples of these types of brain damage are outlined below.

Traumatic brain injury

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

See severe head injury for more information.

Non-traumatic brain 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 will begin 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 aneurysm

Progressive brain damage

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