It has long been thought that parkinsonism is the result of a concussion or another form of head injury, but this is not the case. The precise cause of parkinsonism is not yet known, and several factors seem to be able to play a role. Hereditary and non-hereditary factors can contribute. It is not clear whether having a concussion at a younger age is not having an influence on the disease later on. It is also unclear if very frequent brain injury (such as with boxers) plays a role in Parkinson's disease, but it is probably not healthy for the brain.