The causes of psoriasis have not yet been fully researched. It is known that several genes play an important role. However, only the predisposition and not the disease itself is hereditary: And so it is possible for neither father nor mother to have psoriasis, but their child is still diagnosed. 

Conversely, a hereditary predisposition alone does not necessarily mean that the disease will occur. Other internal or external factors are needed in order to trigger the condition: Injuries or persistent friction are just as possible as psychological strain. Infectious diseases, metabolic and hormonal disturbances, and also environmental influences can all be factors that trigger psoriasis.