Playing a contact sport like football is bound to lead to injuries, but new research into the long-term effects of concussions shows how much the game can cost players.

In the past, dramatic bodily injuries such as broken limbs, necks and fractured skulls were the ones everyone was worried about. However, as those types of injuries decreased and more studies were done on retired players, more emphasis has been put on concussions and their consequences.

A concussion is a relatively minor head trauma and one of the most common types of brain injuries. Lots of things can cause a concussion – a soccer ball to the head, a right hook to the jaw or the whiplash caused by a car crash. The results can be varied, from dizziness and nausea to trouble sleeping and irritability.

Your brain doesn’t have direct contact with your skull. Instead, it is suspended in a substance called cerebrospinal fluid, which acts as a shock absorber and protects it from minor traumas. This is why you don’t injure your brain every time you bump your head.

However, in more extreme cases, the cerebrospinal fluid isn’t enough. More severe impacts can cause your brain to move around inside your skull, or even hit the skull’s inner surface. This can upset, and even damage, neural pathways and delicate brain tissue, causing a number of different symptoms depending on where and how the brain was affected.

Concussions are more serious in children because their brains are still developing. The symptoms can be more severe, and the risk of long-term damage is higher.

In adults, one concussion is usually not cause for worry. If the symptoms seem severe, a visit to the hospital might be in order, but death as a direct result is very rare.

The main danger for adults is repeated trauma. The more concussions a person has, the more likely they are to experience issues. For example, multiple concussions have been found to increase your risk of depression, dementia and Parkinson’s disease later in life.

These findings have led to an increased call for better helmets and even changes to the rules of contact sports like football to protect players. The National Football League responded to this research by implementing two significant rule changes for the 2015-2016 season in an effort to reduce the number of concussions occurring during gameplay.