Cysts form when fluid, air, or semi-solid material gets trapped in a pocket of tissue with nowhere to go. The exact mechanism depends on where the cyst develops, but the underlying pattern is the same: something that should drain or be shed gets sealed off, and a sac builds up around it. Most cysts are noncancerous and develop slowly, sometimes over weeks or months before you notice them.
Skin Cysts: Trapped Cells and Blocked Glands
The most common cysts people find on their body are epidermoid cysts, which form just under the skin’s surface. Your outer layer of skin constantly sheds dead cells. Sometimes, instead of flaking off, those cells migrate deeper into the skin. Once trapped below the surface, they form the walls of a small sac and begin secreting keratin, a thick protein your body normally uses to build skin, hair, and nails. That keratin accumulates inside the sac, creating the firm, round lump you can feel. If you’ve ever heard of a cyst leaking a thick, cheese-like substance, that’s the built-up keratin.
Skin irritation or injury to a hair follicle often triggers this process. A cut, a scrape, a surgical wound, or even chronic friction from clothing can push skin cells inward rather than outward.
A related type, sometimes called a sebaceous cyst, forms when the opening of an oil gland gets blocked. The gland keeps producing its oily substance (sebum) but the oil has no way to reach the skin’s surface, so it pools beneath it and a cyst grows around the trapped material.
How Ingrown Hairs Lead to Cysts
When a hair curls back under the skin instead of growing straight out, it can plug the hair follicle. That blockage creates a small pocket between the clogged surface and the base of the follicle. Dead skin cells and keratin collect in that pocket. At the same time, your immune system recognizes something is wrong and sends fluid to the area. The combination of fluid, protein, and cellular debris gets sealed in by the ingrown hair, and a cyst forms.
This is especially common in areas prone to shaving or friction, like the bikini line, neck, and face. People with curly or coarse hair are more susceptible because their hair is more likely to curve back into the skin after being cut.
Ovarian Cysts: A Normal Cycle Gone Slightly Off
Ovarian cysts are extremely common and usually develop as part of the menstrual cycle. There are two main types, and both involve the small fluid-filled sac (follicle) that holds a developing egg.
A follicular cyst forms when the follicle doesn’t rupture to release the egg at ovulation. Instead of breaking open, it keeps growing and fills with fluid. These are the most common ovarian cysts and typically resolve on their own within one to three cycles.
A corpus luteum cyst works differently. After a follicle successfully releases an egg, it shrinks and starts producing hormones needed for a potential pregnancy. But sometimes the opening where the egg escaped seals shut. Fluid builds up inside the now-closed follicle, forming a cyst. Most corpus luteum cysts also disappear without treatment, though they can occasionally grow large enough to cause pain or, rarely, twist the ovary.
Ganglion Cysts: Fluid From Joints and Tendons
Ganglion cysts are the rubbery bumps that tend to appear on wrists, hands, and feet, usually near a joint or along a tendon. They’re filled with a thick, jelly-like fluid similar to the lubricating fluid found inside joints. The cyst grows out of the joint lining or tendon sheath on a small stalk, almost like a water balloon attached to the joint.
The honest answer is that nobody fully understands why ganglion cysts develop. Repetitive joint stress and prior joint injuries seem to increase the likelihood, and they’re more common in women and in people between ages 20 and 40. They can fluctuate in size, sometimes growing larger with increased joint activity and shrinking with rest.
Risk Factors That Make Cysts More Likely
Certain factors raise your chances of developing cysts repeatedly. Heredity plays a significant role, particularly with severe acne. About 20% of people with acne develop a severe form involving deep nodules and cysts, and family history is one of the strongest predictors for these cases. Hormonal fluctuations, especially around puberty, menstruation, and polycystic ovary conditions, also drive cyst formation both on the skin and internally.
In rare cases, people develop many cysts due to a genetic condition called steatocystoma multiplex. This is caused by a mutation in a gene responsible for building keratin networks in skin cells. The defective keratin disrupts how sebaceous glands function, leading to dozens or even hundreds of small cysts, typically appearing during adolescence on the torso, neck, upper arms, and upper legs.
Cyst vs. Lipoma vs. Abscess
Not every lump under the skin is a cyst. Lipomas are fatty growths that feel soft, rubbery, and doughy. They slide easily under the skin when you press them, are painless, and blend with your natural skin color. Cysts, by contrast, feel firmer, like a small balloon under the skin. They may be slightly movable but tend to feel more anchored in place. A cyst sometimes has a tiny dark dot on the surface called a punctum, which is the blocked opening.
An abscess is different from both. It’s a pocket of infection: red, warm, swollen, and painful. If a cyst becomes infected (bacteria get trapped inside), it can look and behave like an abscess, with redness, tenderness, discharge, and sometimes a foul smell. An uninfected cyst is not usually painful.
Why Popping a Cyst Doesn’t Work
Squeezing or cutting into a cyst at home is one of the worst things you can do. It introduces bacteria, raises the risk of infection, and almost guarantees the cyst will return. That’s because a cyst isn’t just a blob of fluid. It has a lining, a sac wall that actively produces the material inside it. If that sac stays in place, the cyst refills over time.
Even professional drainage, where a provider punctures the cyst and removes the contents, is considered a temporary fix. The cyst can come back because the sac wall remains. The only way to prevent recurrence is surgical removal of the entire cyst, including its lining. This is a minor outpatient procedure for most skin cysts, and it significantly lowers the chance of the cyst returning.
Many cysts need no treatment at all. If a cyst isn’t painful, infected, or in a cosmetically bothersome location, monitoring it is a perfectly reasonable approach. But if it grows, becomes tender, or shows signs of infection like redness and warmth, having it evaluated sooner rather than later makes removal simpler and reduces the chance of complications.