Subconcussion, or subconcussive head impacts, are head traumas that do not cause immediate symptoms. However, they may cause long-term effects, such as memory problems and depression.

The Centers for Disease Control and Prevention (CDC) define subconcussive head impacts as impacts to the head that cause sudden brain movement without neurological symptoms.

Such impacts may include bumps, jolts, or blows. Clashes of heads while playing sports may cause subconcussive head impacts. Scientists remain uncertain about the best response to subconcussive impacts.

This article explains the differences between subconcussion and concussion, risk factors, and potential complications. It also details chronic traumatic encephalopathy (CTE) and how to help prevent and respond to concussions.

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As the CDC explains, subconcussion and concussion are types of brain injury. Concussions cause neurological symptoms, whereas subconcussions are asymptomatic, meaning they do not cause symptoms.

Concussion occurs when the brain moves very suddenly, making it bounce or twist within the skull. This can cause chemical changes in the brain and damage brain cells.

Subconcussions are milder than concussions. However, the cumulative effect may cause measurable changes to brain health.

Anyone can experience a concussion or subconcussion. However, people who play certain sports regularly have an increased risk. According to a 2022 review, risk factors for concussion include:

  • participation in sports such as football, boxing, and soccer
  • car crashes
  • assaults

A concussion can also result from falls or being struck on the head by a falling object.

Doctors cannot yet diagnose subconcussion. This is because subconcussions are asymptomatic, and reliable tests do not yet exist. However, any significant impact to the head could potentially cause a subconcussion.

Scientists still need to determine the effects of subconcussive head impacts. However, there is evidence for a variety of potential effects.

Memory and attention

The research into how repeated subconcussions affect memory and attention remains unclear.

One 2016 study compared children engaging in high and low contact sports. The study did not find differences in verbal or visual memory. However, high contact sports did seem to correlate with negatively affected visual motor speed and reaction times.

Contrastingly, a 2019 study found negative short-term effects on memory following boxing sparring sessions. The study participants performed less well on memory tasks following three 3-minute sparring sessions compared with their performances before sparring.

Brain connections

There is evidence that repeated subconcussions can affect brain cells.

According to a review in Environmental Research and Public Health, studies have found correlations between playing soccer and damage to the brain’s white matter. Other studies have found correlations between subconcussions and damaged glial cells (important cells that support neurons, among other functions).

Brain function

The same review discusses evidence that repeated subconcussions could have various negative effects on brain function. This includes effects on:

  • signaling between neurons
  • energy transmission within the brain
  • brain reactivity

Mood and behavior

There is evidence that subconcussions may lead to psychological changes. In particular, subconcussive impacts may be a risk factor for depression.

Learn about the link between concussion and depression here.

Repeated subconcussions may lead to chronic traumatic encephalopathy (CTE). Scientists define CTE as a neurodegenerative condition that can follow reoccurring head impacts over a long period of time.

CTE typically develops gradually, and a person may not experience symptoms until several years after experiencing subconcussions. The symptoms are often similar to other neurodegenerative conditions, particularly Alzheimer’s disease.

Symptoms of CTE include:

  • memory problems
  • changes in behavior or personality
  • speech or movement difficulties

Scientists continue to investigate the link between CTE and subconcussive head impacts.

It is impossible to completely eliminate the risk of subconcussive head impacts. However, some precautionary steps may lower the risk. For instance, the CDC discusses some preventive steps within a sports context. These include:

  • teaching techniques that reduce risks of head injuries
  • encouraging norms of fair and respectful play
  • enforcing rules that make head impacts less likely

Outside a sports context, safe driving can help prevent concussions from car crashes.

Research has also shown that certain exercise programs can reduce the risk of falls, especially in older individuals.

Find balance exercises for seniors here.

The 2022 review provides information about the possible signs of concussion. These include:

A concussion can also cause changes in sleep patterns. An individual with a concussion may sleep more or less than is typical. They may also have difficulty getting to sleep.

Learn whether it is safe to sleep with concussion here.

Scientists remain unsure about the best protocol for subconcussive head impacts. However, the CDC is clear about safety procedures following a concussion.

People can help someone with a concussion by removing them from a situation that could cause further head impacts. For example, a coach should remove an athlete from the game if they suspect a concussion.

The next step is to record the following details:

  • the cause and force of the head impact
  • any loss of consciousness, including its duration
  • any post-injury memory loss
  • any post-injury seizures
  • any past concussions

This information can be extremely important when it comes to treating concussions.

Learn more about what to do for a concussion here.

Anyone with a concussion should seek medical attention.

Some concussions require urgent medical attention from first responders. A person with the following symptoms should receive medical care immediately:

The above symptoms could indicate bleeding within the brain. People with these symptoms may need someone else to contact the emergency services for them.

Learn about brain bleed symptoms here.

Scientists do not know the outlook for people who experience subconcussions. However, the outlook for people with concussions is clearer.

In the shorter term, many people experience reductions in their symptoms. In other cases, symptoms can last for weeks or months after the injury. This condition is called post-concussion syndrome. It lasts for an average of 7 months.

In the longer term, research suggests that around 17% of people who experience repeated concussions develop CTE.

Learn about concussion recovery here.

Subconcussions are milder than concussions and do not cause obvious symptoms. Trauma to the head can cause subconcussions, so athletes in certain contact sports have an increased risk.

Repeated subconcussions may damage parts of the brain, affecting brain function. Although the long-term effects of subconcussions are unclear, they may lead to CTE.

Taking steps to avoid head trauma is key to reducing the risk of subconcussions. Sports coaches may wish to teach techniques that minimize blows to the head, for example.

If someone experiences head trauma, they should receive medical attention immediately.