Cysts form when fluid, air, or semi-solid material gets trapped inside a pocket of tissue that isn’t supposed to be there. The specific trigger depends on the type of cyst and where it develops, but the underlying pattern is almost always the same: something that should drain or dissolve instead gets walled off by the body, creating a slow-growing sac. Some cysts are caused by blocked glands, others by hormonal shifts, joint stress, infections, or inherited gene mutations.
Skin Cysts: Trapped Cells and Blocked Glands
The most common cysts people notice are the firm, round lumps that develop just under the skin. These are usually epidermoid cysts (often incorrectly called sebaceous cysts). They form when skin cells that normally shed from the surface migrate deeper into the skin instead. Once buried, those cells keep doing what skin cells do: they multiply and produce a protein called keratin. That keratin has nowhere to go, so it accumulates inside a sac that grows slowly over months or years. The result is a painless, movable lump filled with thick, cheese-like material.
Skin irritation, a minor cut, or damage to a hair follicle can kick off this process. That’s why epidermoid cysts often appear on the face, neck, and trunk, areas prone to friction and minor trauma. True sebaceous cysts, which fill with oily sebum rather than keratin, are actually rare and typically associated with a specific condition called steatocystoma multiplex.
One important distinction: when a skin cyst becomes red, swollen, and painful, it’s usually not infected. The cyst wall has ruptured internally, spilling its contents into surrounding tissue and triggering an inflammatory reaction. This looks a lot like an abscess, but the treatment can differ. An abscess is a true collection of pus caused by bacteria, typically appearing as a tender, warm red nodule. A ruptured cyst is an irritation response, not an infection.
Ovarian Cysts: A Normal Cycle Gone Slightly Off
Most ovarian cysts are a byproduct of menstruation and form without any underlying disease. Every month, the ovaries grow small fluid-filled structures called follicles that produce hormones and release an egg at ovulation. When that process doesn’t go exactly to plan, a cyst can develop. There are two common types.
A follicular cyst forms when a follicle doesn’t rupture to release its egg. Instead, it keeps growing and fills with fluid. A corpus luteum cyst forms after the egg has been released. Normally, the empty follicle shrinks and produces hormones to support a potential pregnancy. But if the opening seals shut, fluid accumulates inside, creating a cyst. Both types are called functional cysts, and most resolve on their own within a few menstrual cycles without causing symptoms.
Hormonal fluctuations are the primary driver. Conditions that affect hormone balance, like polycystic ovary syndrome, can increase the frequency and number of ovarian cysts.
Ganglion Cysts: Joint Stress and Fluid Leaks
Ganglion cysts are the rubbery lumps that pop up near joints and tendons, most commonly on the wrist. They form when fluid from a joint capsule or tendon sheath leaks into surrounding tissue. The fluid collects in a sac that has no true lining of its own, distinguishing it from other cyst types.
Trauma to a joint, repetitive motion, and general wear and tear on connective tissue all contribute. The exact mechanism isn’t fully understood, but the prevailing explanation involves a combination of mucoid degeneration (a breakdown of connective tissue) and herniation, where the joint lining bulges outward under pressure. People who use their wrists heavily, whether from typing, gymnastics, or manual labor, develop these more frequently.
Pilonidal Cysts: Hair, Friction, and Sitting
Pilonidal cysts develop near the tailbone, in the crease between the buttocks. They’re most common in young men and typically appear during adolescence or early adulthood. The leading explanation is that the motion of the gluteal folds combined with gravity creates a pulling force on hair follicles, distorting them. Loose hairs get driven into the skin, triggering an inflammatory response that forms a cyst or a sinus tract.
While some researchers have argued for a congenital origin, where remnants from embryonic development persist near the base of the spine, the condition is now widely considered acquired. The strongest risk factors are practical ones: obesity, prolonged sitting, coarse or stiff body hair, and poor hygiene in the area. The condition was famously common among military truck drivers in World War II, earning the nickname “jeep driver’s disease.”
Kidney Cysts: Genetic Mutations
Not all cysts are caused by blocked ducts or hormonal cycles. Polycystic kidney disease is a genetic condition in which thousands of fluid-filled cysts grow throughout the kidneys, gradually impairing their function. The disease is caused by mutations in genes that provide instructions for proteins involved in normal kidney development and cell signaling.
The most common form, autosomal dominant polycystic kidney disease, requires only one copy of a mutated gene to develop. If a second mutation occurs in the remaining healthy copy, cysts tend to grow faster and the disease becomes more severe. A rarer form, autosomal recessive polycystic kidney disease, involves a different gene and typically appears in infancy or childhood. In both cases, the cysts are not preventable because the underlying cause is encoded in a person’s DNA.
Cysts Caused by Infection
Certain parasitic infections can produce cysts in muscle, brain, and eye tissue. The most well-known example is cysticercosis, caused by swallowing eggs from the pork tapeworm. Once ingested, the larvae migrate through the bloodstream and embed in tissues, forming cysts called cysticerci. When cysts develop in the brain, the condition is called neurocysticercosis, and it’s one of the leading causes of seizures worldwide in regions where the parasite is common. This type of cyst is entirely preventable through food safety and sanitation.
Reducing Your Risk of Skin Cysts
You can’t fully prevent cysts, especially those driven by genetics or normal hormonal cycles. But for skin cysts specifically, a few habits lower your odds. Washing regularly with mild, non-comedogenic cleansers helps keep pores and glands clear. Treating cuts, scrapes, and skin injuries promptly reduces the chance that damaged skin cells will migrate inward and form a cyst. If you’re prone to hormonal acne or cyst formation, managing hormone fluctuations through a dermatologist can make a meaningful difference.
Avoid squeezing or picking at existing cysts. Rupturing the wall internally turns a painless lump into an inflamed, painful problem, and increases the likelihood it will recur in the same spot.