Picking out a black hard substance from the back may be caused by grease scale, acne and dilated holes. 1. Grease scale: Young people have too much oil on the surface of their skin, especially more on the face and scalp. It can also be found on the chest and back. If not cleaned in time, dust in the air will mix with sebum, thus forming gray dirt and grease scale. At this time, you can squeeze at the opening of the hair follicle to squeeze out the greasy dirt from it. 2. Acne: It is a chronic inflammatory skin disease of the sebaceous glands of the hair follicles. Infections of the sebaceous glands of the hair follicles and excessive sebum secretion lead to blockage of the hair follicles and sebaceous glands. Bacteria and mites multiply in the glandular ducts, and oxidative reactions occur in the exposed areas of acne. In severe cases, known as polymer acne, the infected area is also deep, resulting in a hard black color. 3. Dilated foramen ovale: a condition formed by the enlargement of the funnel part of the skin follicle, clinically manifested as a single, blackhead pimple-like lesion. It can also lead to the back picking out a black hard thing. When you pick out a black hard object on your back, you should go to the dermatology department of a regular hospital and ask the doctor to diagnose and treat it correctly.