May be a sebaceous gland cyst. (Sebaceous cyst) commonly known as "powder tumor", mainly due to obstruction of sebaceous gland drainage tube, sebaceous gland sac epithelium is gradually increased by the content of the expansion of the retention of cysts. It is characterized by a slow-growing benign lesion. There is a white bean dregs-like secretion in the capsule. It can occur at any age, but it is more common in young adults, and it occurs in the head, neck and chest and back. Sebaceous cysts protrude from the surface of the skin and generally have no symptoms. For example, there may be pain and suppuration during secondary infection. The cause of the disease is obstruction of the sebaceous gland duct, which leads to accumulation of sebaceous gland excretion barrier. Sebaceous gland duct obstruction is mostly caused by dust blockage and bacterial infection. Sebaceous cysts protrude from the surface of the skin and occur in areas rich in sebaceous glands, such as the scalp, face, chest and back, and most of them grow slowly. When there is no infection, the patient generally has no symptoms. The masses are spherical, single or multiple, varying in size, ranging from a few millimeters to nearly 10 centimeters. Medium hardness, elastic, higher than the leather surface, adhesion to the skin, not easy to push, smooth surface, no fluctuation, the central part of the needle has a large umbilical hole concave opening, blue-black, shaped like a needle acne, extrusion can be Out of the bean curd or mud-like contents, the contents are sebum and broken sebaceous gland cells, often with rancid smell. Sebaceous gland cysts are extremely rare, but they are susceptible to secondary infection. If they are complicated, they may have red, swollen, hot and painful inflammatory reactions. The cyst can rupture under external force and temporarily resolve, but it will form a scar and is prone to recurrence. Need to be diagnosed according to clinical manifestations and related examinations.