Concussion is the sudden but short-lived loss of mental function that occurs after a blow or other injury to the head. It is the most common but least serious type of brain injury.

The medical term for concussion is minor traumatic brain injury.

Symptoms of concussion include brief:

• loss of consciousness after the head injury
• periods of memory loss
• disturbances in vision, such as "seeing stars" or blurry vision
• a period of confusion, a blank expression, or a delay in answering questions immediately after the head injury

If a brain scan is carried out, concussion is only diagnosed if the scan is normal – for example, there is no bleeding or swelling of the brain.

When to seek medical help

Concussion should only be diagnosed by a health professional trained in assessing patients with head injury. They will be able to rule out serious brain injury that needs a brain scan or surgery.

You should visit your nearest accident and emergency (A&E) department if you or someone in your care has a head injury and develops the following signs and symptoms:

• loss of consciousness, however brief
• memory loss, such as not being able to remember what happened before or after the injury
• persistent headaches since the injury
• changes in behaviour, such as irritability, being easily distracted or having no interest in the outside world – this is a particularly common sign in children under five
• confusion
• drowsiness that occurs when you would normally be awake
• loss of balance or problems walking
• difficulties with understanding what people say
• difficulty speaking, such as slurred speech
• problems with reading or writing
• vomiting since the injury
• problems with vision, such as double vision
• loss of power in part of the body, such as weakness in an arm or leg
• clear fluid leaving the nose or ears (this could be cerebrospinal fluid, which surrounds the brain)
• sudden deafness in one or both ears
• any wound to the head or face

Anyone drunk or high on recreational drugs should go to A&E if they have a head injury as it's easy for others around them to miss the signs of a more severe injury.

Phone 999 for an ambulance immediately if the person:

• remains unconscious after the initial injury
• is having a seizure or fit
• is bleeding from one or both ears
• has been vomiting since the injury
• is having difficulty staying awake, speaking, or understanding what people are saying

Certain things make you more vulnerable to the effects of a head injury. These include:

• being aged 65 or older
• having previously had brain surgery
• having a condition that makes you bleed more easily, such as haemophilia
• having a condition that makes your blood more prone to clotting, such as thrombophilia
• taking anticoagulant medication, such as warfarin or aspirin, to prevent blood clots

There are things you can do at home to help relieve concussion symptoms, including:

• apply a cold compress to the injury to reduce swelling – a bag of frozen peas wrapped in a towel will do
• take paracetamol to control any pain – do not use non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or aspirin, as these can cause bleeding
• avoid drinking alcohol or taking recreational drugs

Read more about how concussion is treated, including information on self care tips and when you can return to playing sport.

Recovery

After experiencing concussion, careful monitoring is needed. This is usually for 48 hours.

This is because the symptoms of concussion could also be symptoms of a more serious condition, such as:

• subdural haematoma – bleeding between the skull and the brain
• subarachnoid haemorrhage – bleeding on the surface of the brain

Outlook

While the medical term "minor traumatic brain injury" can sound serious, the actual extent of damage to the brain is usually minimal and does not cause long-term problems or complications.

There is evidence that repeated episodes of concussion could cause long-term problems with mental abilities and trigger dementia. This type of dementia is known as chronic traumatic encephalopathy (CTE).

However, this seems to only be a significant risk for professional athletes who experience repeated episodes of severe concussion, such as boxers – CTE is sometime nicknamed "boxer's brain".

Post-concussion syndrome (PCS) is a poorly understood condition where symptoms of concussion can last for weeks or months afterwards.

Read more information about PCS as a complication of concussion.

Who's at risk?

Most cases of concussion occur in children and teenagers aged 5 to 14, with the two most common causes being sporting and cycling accidents.

Falls and motor vehicle accidents are a more common cause of concussion in older adults.

People who regularly play competitive team sports such as football and rugby have a higher risk of concussion.

Read more information about the causes of concussion and tips on preventing concussion.