The causes of hard bumps on the back of the neck are boils, acne, sebaceous cysts, lipomas, and normal spines. 1. Boils. It is caused by bacterial infection of individual sebaceous glands or hair follicles of human skin, including Staphylococcus albicans, Staphylococcus aureus, and Streptococcus hemolyticus. In the early stages, they may appear as inflammatory pimples, red hard nodules, and painful when pressed. 2. Acne. With sebaceous glands overproduction of pore blockage bacterial infection and inflammation, mainly manifested as pustules, inflammatory papules, nodules and cysts, can be used externally with vita-acid ointment, oral tetracycline drugs for treatment. 3. Sebaceous cysts. Also known as acne, is the sebaceous gland conduit blockage, sebaceous gland epithelium gradually expand the formation of a benign lesion, the growth is relatively slow, the cysts within the secretion of soybean residue, protruding from the surface of the skin, if the secondary infection will be painful, pus. 4. Lipoma of the back of neck. Usually asymptomatic, only manifested as a lump in the back of the neck, need ultrasound and cervical spine radiography. 5. Normal spinous processes. Since the spinous processes of the seventh cervical vertebrae are longer and more obvious when the head is bowed, some patients may mistake them for abnormal tissues. Avoid scratching and squeezing before diagnosis to avoid infection, go to a regular hospital for consultation, and use medication under the guidance of a physician.