There is no single cause of dementia. Rather, a combination of multiple factors is associated with the development of dementia. Family history and lifestyle factors, such as exercise patterns, dietary habits, and stress levels, are examples of risk factors that may contribute to the onset of dementia.
Risk factors are characteristics which increase the likelihood of developing a disease. Their presence does not guarantee the development of the disease in question. For example, not everyone who smokes develops heart disease and not everyone with heart disease has been a smoker. However, a person who smokes is more likely to develop heart disease.