Endogenous stimuli refer to complex pathological changes within the organism caused by adverse external stimuli. Psoriasis occurs due to endogenous stimuli triggered by various adverse external stimuli on the basis of genetic susceptibility. The endogenous stimuli in psoriasis may be related to self-antibodies, cytokines with cytotoxic activity against antigens, toxins produced by viruses and bacteria, and certain metabolic substances in tissues that are stress-induced."