Genetic and external causes
The outbreak of psoriasis is associated with genetic susceptibility, which is transmitted via multiple genes. Because the disease is multifactorial, it may leap over more than a few generations. Not everyone with the hereditary predisposition shows psoriasis symptoms.
In addition to the underlying genetic predisposition to the illness, external factors such as infections, skin damage, excessive alcohol consumption, smoking, obesity and stress have an impact on the outbreak of psoriasis. With some patients these factors also make psoriasis symptoms worse. Regular physical activity is the only factor that has been shown to reduce the incidence of psoriasis. In addition, triggering factors should be avoided. The outbreak of psoriasis can occur at any age. Two peaks of incidence occur at the ages 15–25 and 50–65. Adolescent and elderly psoriasis have largely different genetic backgrounds.