A cyst typically feels like a small, round, firm lump just under the skin that moves slightly when you press on it. Most cysts range from pea-sized to about an inch across, grow slowly, and are painless unless they become inflamed or infected. If you’ve noticed a bump like this, there’s a good chance it’s a cyst, but the type, location, and symptoms all matter in figuring out what you’re dealing with.
What a Skin Cyst Feels and Looks Like
The most common type of cyst you can actually see and touch is an epidermoid cyst, sometimes still called a sebaceous cyst (though that name is technically inaccurate, since these cysts don’t involve oil glands). Epidermoid cysts account for roughly 80 to 90 percent of all skin cysts, and they’re the fifth most common skin diagnosis in the United States. They occur about twice as often in men as in women.
A typical epidermoid cyst is a round, hard lump sitting just beneath the surface of the skin. It’s enclosed in its own sac, which is what distinguishes it from other types of lumps. You can usually roll it slightly under your finger. The skin over it looks normal or has a small dark dot at the center, which is the opening of the sac. These cysts tend to show up on the face, neck, chest, and upper back, though they can form almost anywhere.
Ganglion cysts are another common type. These develop along tendons or joints, most often on the wrist or hand. They feel firm, smooth, and round, and they may change size over time. A ganglion cyst near a joint can cause aching or discomfort, especially with repetitive motion.
Pilar cysts grow on the scalp and feel very similar to epidermoid cysts. Baker’s cysts form behind the knee and can create a sensation of tightness or fullness when you bend your leg.
How a Cyst Differs From Other Lumps
Not every lump is a cyst, so it helps to understand the differences. A cyst is a closed sac filled with fluid, air, or semi-solid material. It has a defined border, grows slowly, and is almost always noncancerous. A tumor, by contrast, is a solid mass of tissue. While many tumors are also benign, they lack the enclosed sac that surrounds a cyst.
An abscess can look similar to a cyst on the surface, but it behaves very differently. An abscess is a pocket of pus caused by a bacterial infection. It usually appears pink or red, feels warm to the touch, and is noticeably painful and swollen. It also tends to develop faster than a cyst. If your lump came on quickly and hurts a lot, an abscess is more likely than a cyst.
One important distinction: cysts can become infected and start to resemble abscesses. A cyst that was once painless but is now red, swollen, and tender may have ruptured or become inflamed. A ruptured cyst can lead to a boil-like infection that needs treatment, so a lump that suddenly changes deserves attention even if it’s been there quietly for months or years.
Signs of an Infected or Inflamed Cyst
Most cysts sit under the skin for a long time without causing any problems. The trouble starts when one becomes inflamed or infected. An inflamed cyst can become painful and swollen even without an active infection. The area around it may turn red, feel warm, and become tender to the touch.
If the cyst ruptures beneath the skin, the contents leak into surrounding tissue and trigger a stronger inflammatory reaction. This can look and feel like a boil: a hot, red, painful lump that may start to drain thick or foul-smelling fluid. At this point, the cyst typically needs professional drainage rather than home care. Squeezing or popping a cyst yourself increases the risk of infection and scarring.
Cysts You Can’t See or Feel
Not all cysts are on the surface. Cysts commonly form inside the breasts, ovaries, kidneys, and other internal organs, and these are harder to detect on your own because you can’t see or touch them. Many internal cysts produce no symptoms at all and are found incidentally during imaging for something else.
Ovarian cysts are a good example. Most cause no symptoms and resolve on their own within a few menstrual cycles. But a large ovarian cyst can cause a dull ache or sharp pain on one side of the lower abdomen, a feeling of fullness or pressure in the belly, and bloating. If an ovarian cyst ruptures or twists, it can cause sudden, severe pelvic pain, sometimes with fever, vomiting, rapid breathing, or cold and clammy skin. These are signs of a medical emergency.
Breast cysts are also common and often feel like a smooth, round, movable lump in the breast. They can be tender, especially before your period. A clinical exam alone can’t reliably distinguish a breast cyst from a solid mass, which is why imaging is typically the next step.
Kidney cysts are usually discovered during an ultrasound or CT scan done for another reason. Small, simple kidney cysts rarely cause symptoms and don’t require treatment. Larger ones can occasionally cause pain in the side or upper abdomen.
How Cysts Are Diagnosed
If you find a lump and aren’t sure what it is, a healthcare provider will typically start with a physical exam. For skin cysts, the location, texture, and mobility of the lump often point toward a diagnosis. But physical exams have limits, especially for internal lumps or breast lumps where the stakes of misidentification are higher.
Ultrasound is the most common tool for evaluating cysts. It can show whether a lump is filled with fluid (which points to a cyst) or solid (which could be a benign growth or, less commonly, something that needs further evaluation). For breast lumps, mammography can detect large cysts and clusters of small ones, though very small cysts may not show up on a mammogram.
In some cases, a provider will perform a fine-needle aspiration, inserting a thin needle into the lump to draw out fluid. If straw-colored, non-bloody fluid comes out and the lump disappears completely, that confirms a cyst and no further testing is needed. If the fluid is bloody, or the lump doesn’t go away after aspiration, a tissue sample may be taken to rule out other conditions.
What Symptoms Should Prompt an Evaluation
A small, painless, slow-growing lump that’s been stable for a while is rarely urgent. But certain changes warrant a closer look:
- Rapid growth. A lump that doubles in size over weeks rather than months.
- Pain, redness, or warmth. Signs of inflammation or infection.
- Drainage. Fluid or pus leaking from the lump, especially if it smells foul.
- A lump that doesn’t move. Cysts are typically mobile under the skin. A fixed, hard mass is worth investigating.
- Location in the breast. Any new breast lump should be evaluated with imaging, since physical exams alone can’t distinguish cysts from solid masses.
- Sudden severe abdominal or pelvic pain. This could indicate a ruptured or twisted ovarian cyst and needs immediate attention.
Most cysts are harmless and many don’t need treatment at all. Small skin cysts that aren’t bothering you can simply be left alone. If a cyst is cosmetically bothersome, keeps getting inflamed, or is in a location where it gets irritated by clothing or movement, minor surgical removal is straightforward and usually done in a clinic setting. Internal cysts are often monitored with periodic imaging to make sure they aren’t growing or changing.