Cysts are sacs or capsules that form in the skin or inside the body. They may contain fluid or semisolid material. Although cysts can appear anywhere in the body, most frequently they live in the skin, ovaries, breasts or kidneys. Most cysts are not cancerous.
Common locations of cysts include:
Skin — Two types of cysts commonly occur underneath the skin, epidermoid cysts and sebaceous cysts. Both usually appear as flesh-colored or whitish-yellow smooth-surfaced lumps. Epidermoid cysts form when surface skin cells move deeper into the skin and multiply. These cells form the wall of the cyst and secrete a soft, yellowish substance called keratin, which fills the cyst. Sebaceous cysts form inside glands that secrete an oily substance called sebum. When normal gland secretions become trapped, they can develop into a pouch filled with a thick, cheese-like substance. Common sites include the back of the neck, the upper back and the scalp.
Wrists — Ganglion cysts develop as rubbery or soft swellings, usually in response to a minor injury that triggers excess joint fluid to collect in a saclike structure next to the joint. Ganglion cysts also can occur on the fingers or feet.
Knees — A Baker's cyst is a pouch of joint fluid that collects behind the bend of the knee. Because of its location, this cyst may cause the knee joint to feel swollen or tight. In most people, Baker's cysts are linked to arthritis or knee injury.
Ovaries — An ovarian follicle that doesn't release its egg may form a cyst on the ovary. These cysts are not harmful and usually disappear after two to three months.
Breasts — Breast lumps may be either cystic or solid. Breast cysts are almost always benign (non-cancerous).
Vagina — Bartholin's gland cysts may develop in one of the Bartholin's glands, which lie just inside the vaginal canal and produce a protective, lubricating fluid. The buildup of secretions or infections inside one of the Bartholin's glands can cause the gland to swell and form a cyst.
Cervix — Nabothian cysts develop when one of the mucous glands of the cervix becomes obstructed.
Kidneys — Solitary cysts (also known as simple cysts) are the most common type. They appear as fluid-filled pouches and usually do not cause any symptoms. About 25% of Americans older than age 50 have this type of cyst. Some people inherit the tendency to develop many kidney cysts, a condition called polycystic kidney disease, which often causes high blood pressure and can lead to kidney failure.