Brain health basics
Understanding the two broad categories
Updated 04 October 2026 · Educational reference
Summary
- Traumatic brain injuries result from an external force or impact.
- Acquired brain injuries develop after birth from causes such as infection, disrupted oxygen supply, or altered fluid pressure.
- The same event can affect different people in different ways; assessment should be based on symptoms and clinical examination.
- Urgent symptoms after a head injury should never be ignored.
The brain is protected by the skull, membranes, and cerebrospinal fluid, but this protection is not absolute. Injury can affect movement, sensation, speech, memory, attention, mood, alertness, or several of these functions together. Some changes are immediate, while others become noticeable later.
Traumatic brain injuries
A traumatic brain injury occurs when a blow, jolt, penetration, or forceful movement disrupts normal brain function. It may be described as open when the skull and its coverings are breached, or closed when the skull remains intact. A closed injury can still cause significant internal damage.
Possible effects include headache, dizziness, confusion, unusual sleepiness, memory difficulty, changes in balance, sensitivity to light or sound, and altered speech or behaviour. Symptoms can change over time, so observation and professional advice are important.
Common types linked with trauma
Concussion
A mild traumatic brain injury involving a temporary change in brain function. A person does not need to lose consciousness to have a concussion.
Contusion
A bruise to brain tissue, usually caused by a direct force. Swelling or bleeding may occur around the bruised area.
Hematoma
A collection of blood outside a blood vessel. It can place pressure on the brain and may require urgent treatment.
Hemorrhage
Bleeding in or around the brain. The location and amount of bleeding determine the risks and treatment.
Coup and contrecoup injury
Damage may occur beneath the point of impact, on the opposite side, or in both locations as the brain moves inside the skull.
Skull fracture
A break in a cranial bone. A fracture may be linear, depressed, open, or involve the base of the skull.
These terms describe different patterns, but they can overlap. For example, one impact may cause a fracture, contusion, and bleeding at the same time. Imaging and clinical assessment help determine what has happened.
Acquired brain injuries
An acquired brain injury develops after birth and is not caused by a genetic condition or by the ordinary process of development. Causes can include infection, lack of oxygen, stroke, toxic exposure, or pressure changes affecting the brain.
Meningitis
Meningitis is inflammation of the membranes surrounding the brain and spinal cord. It may be caused by viruses, bacteria, fungi, or other conditions. Bacterial meningitis can progress quickly and requires urgent medical care; vaccines help prevent some forms of infectious meningitis.
Hydrocephalus
Hydrocephalus occurs when cerebrospinal fluid builds up in or around the brain. The pressure and symptoms vary with age and cause. Head growth in babies, repeated vomiting, unusual sleepiness, headaches, vision changes, or altered thinking should be assessed by a clinician.
Hypoxia and anoxia
Hypoxia means that the brain receives too little oxygen; anoxia means that the oxygen supply is absent or nearly absent. Causes may include breathing failure, cardiac arrest, severe blood loss, poisoning, or other emergencies. Brain cells can be injured quickly when oxygen delivery is interrupted.
When to seek urgent help
After a head injury, seek emergency help for worsening headache, repeated vomiting, increasing confusion, a seizure, weakness or numbness, unequal pupils, trouble speaking, unusual difficulty staying awake, fluid or blood from the nose or ears, or any loss of consciousness. Do not drive someone with serious symptoms yourself if emergency services are available.
For less urgent concerns, contact a qualified healthcare professional. A person recovering from concussion or another brain injury may need carefully paced activity, follow-up, and support with sleep, concentration, movement, or school and work tasks.
Questions and answers
Are all brain injuries caused by a blow to the head?
No. Traumatic injuries follow an external force, while acquired injuries can result from infection, oxygen deprivation, stroke, toxic exposure, or other medical causes.
Can a person have a brain injury without losing consciousness?
Yes. Loss of consciousness is not required for concussion or another traumatic brain injury. Symptoms and examination are more useful than that single feature.
Do symptoms always appear immediately?
No. Some symptoms are immediate and others become clearer over hours or days. Any worsening or worrying change after an injury needs medical advice.
Is a concussion the same as a contusion?
No. A concussion describes a temporary change in brain function, while a contusion is a bruise to brain tissue. They can occur together.
Can this page diagnose a brain injury?
No. Diagnosis may require an examination and, when appropriate, imaging or other tests. Use this page for vocabulary and general orientation only.
Further reading
Continue with the wider guides on the cerebral cortex, the central nervous system, memory, and sleep.