There are various causes of head injuries, most of which can result in both external and internal damage. Roughly 50 percent of internal head injuries (traumatic brain injuries) are caused by accidents that involve automobiles, motorcycles, bicycles or pedestrians, according to the National Institute of Neurological Disorders and Stroke (NINDS).

Head injuries sustained during an automobile-related accident can be closed (e.g., if the head hits the steering wheel or other hard object) or open (e.g., if a piece of debris penetrates the skull and enters the brain). People who fail to take proper safety precautions (e.g. wearing a seatbelt in a car, wearing a helmet when riding a bicycle or motorcycle) have a greater risk of head injury than those who take such precautions. Transportation-related accidents (those that involve cars, motorcycles, bikes and pedestrians) are the most common cause of brain injury in people under the age of 75, according to NINDS.

Other potential causes of head injuries include:

• Falls and other accidents. Falls are the leading cause of hospitalization due to brain injury among people older than 65 years, according to the U.S. Centers for Disease Control and Prevention (CDC). Children are also susceptible to falls and accidents around the house. Most childhood falls result in external injuries rather than internal injuries, which may appear more serious but are often less severe than internal injuries.
  
  
• Contact sports. The CDC estimates that 300,000 brain injuries, typically concussions, result from sports-related activities each year. People who play contact sports, such as football, hockey and boxing, are most at risk. There is evidence that people who play contact sports are also at risk for a potentially fatal condition called second impact syndrome. This rare condition occurs when the brain sustains a series of minor blows within a short space of time.
  
  
• Violence-related injuries. Twenty percent of head injuries are caused by violence, including domestic abuse, child abuse and gun-related crime, according to NINDS. Although firearms cause only 10 percent of brain injuries, they cause 44 percent of brain injury-related death, according to the CDC. The majority of gun-related brain injuries occur as a result of suicide attempts.
  
  
• Alcohol abuse. Intoxication increases the likelihood of engaging in risky behavior, which, in turn, increases the risk of sustaining a head injury. According to NINDS, half of all head injuries involve alcohol use in some way.