If the back of the head is covered with pain and localized redness, it may be caused by folliculitis. You need to take oral antibiotics for symptomatic treatment, such as cefixime or cefradine. You can also disinfect the surface of the folliculitis with iodophor and apply an ointment with antibiotics, such as erythromycin or Bactrim, etc. If there is no inflammation, you need to touch the texture of the lump. If the lump is hard, it may be a sebaceous cyst, mainly due to the formation of a lump with a hard texture and a tofu-like substance inside after the opening of the sebaceous gland is blocked. After the diagnosis of a sebaceous cyst, early removal is recommended, as there is a risk of secondary infection and abscess formation after a long period of time. If the mass is soft, it may be a lipoma, which is a mass formed due to subcutaneous fat hyperplasia, and can be removed surgically if the mass is small and affects the appearance.