The most common clinical condition in which cysts appear on the back is sebaceous cysts. This is mainly due to blockage of the sebaceous glands or hair follicle openings on the back, which subsequently causes sebaceous secretions that cannot be eliminated, thus accumulating and forming a cyst wall package. In case of secondary infection, because it is a confined environment, the contents usually cause anaerobic bacterial infection afterwards, so it causes smelly symptoms. When there is no infection, it usually appears as a tofu-like form. Sebaceous cysts require prompt surgical removal to avoid infection. Rare back cysts are mainly epidermoid cysts. For smaller or solitary epidermoid cysts with no obvious clinical symptoms, they can usually be left untreated and closely observed. If they appear to increase in size or develop local discomfort, they usually need to be surgically removed. The exact cause of epidermoid cysts is not well understood clinically, or the cause of their development is uncertain.