A circumstance that spurs the development of Parkinson’s disease. This may be repeated head trauma, as in the case of the former heavyweight boxing champion muhammad ali, or exposure to chemical toxins such as pesticides. As Parkinson’s disease appears to develop as an intersection of various genetic and environmental (internal and external) factors, there are likely numerous possible trigger events. Most people probably do not know what caused the disease’s development. Limiting exposure to known risk factors for Parkinson’s disease makes sense, although the extent to which these are trigger events remains uncertain.