called keratin.They may occur anywhere on body but scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts. Blocked sebaceous glands, swollen hair follicles and excessive testosterone production will cause such cysts.
Generally no treatment is required but they become painful then it means they are infected, Please keep the area clean and apply some warm compresses and topical antiseptics. Also wear loose-fitting cotton clothing and use an antibacterial soap or mild soap like dove. Avoid any kind of cosmetics. Topical antibiotics such as mupirocin or Neosporin are also useful. In case the symptoms persist then oral antibiotics and excision and surgical excision by traditional wide excision, minimal excision, and punch biopsy excision may be required.