Lipoma vs Cyst: What Causes Lumps Under the Skin, How to Tell Them Apart, Which Need Removal, and Why You Should Not Squeeze Them
A lump you can feel under the skin is one of the most common reasons patients see a doctor. The two most frequent groups are a lipoma (fatty lump) and a subcutaneous cyst. Most are benign and not dangerous, yet many people worry that the lump is cancer, and quite a few try to squeeze a cyst themselves until it becomes inflamed and filled with pus. In this article, a dermatologist explains how these two groups differ, what types of cyst exist, which lumps need to be checked promptly because they may be malignant, and why minor surgery by a doctor to remove the whole sac works better and is safer than handling it yourself.
What is a lipoma (fatty lump under the skin)?
A lipoma forms when mature fat cells (mature adipocytes) grow together into a lump in the fat layer beneath the skin. It is the most common benign fatty tumor. Its typical features are:
Soft and rubbery when pressed, and movable under the skin when you push on it
Painless under normal conditions, and it grows very slowly over years
Common on the back of the neck, back, shoulders, arms and thighs
There are several kinds of lipoma, for example angiolipoma, which is often painful and appears as several lumps; lipomas that lie deep beneath the fascia or within muscle; and, in some people with many lipomas across the body, a link to a genetic condition such as familial multiple lipomatosis, or a form in which the lipomas are painful together with other symptoms (adiposis dolorosa). The doctor will assess these further.
What is a subcutaneous cyst, and what types are there?
A cyst is a sac with a lining wall and material inside it. People often call every one of them a "sebaceous cyst", but that term is not quite accurate, because the common cysts do not come directly from the sebaceous glands. Common types include:
Epidermoid cyst, a sac lined with skin cells and filled with thick, whitish-yellow keratin that looks like cheesy debris. It often has a small opening (punctum) at the center and is common on the face, neck, back and trunk.
Pilar (trichilemmal) cyst of the scalp, which is firm and smooth with no opening. It usually appears on the scalp and runs in families.
Milia, tiny, shallow white keratin cysts on the skin surface.
Steatocystoma multiplex, multiple cysts filled with oily material, usually on the chest and trunk in teenagers.
Unlike a lipoma, a cyst is usually firmer and has an opening, and when it ruptures, thick, foul-smelling material comes out.
Which lumps need to be seen by a doctor promptly?
Most lumps under the skin are benign, but the features below call for an examination as soon as possible, because the lump may not be an ordinary lipoma or cyst, and in some cases a malignant soft-tissue tumor (sarcoma / liposarcoma) must be ruled out.
A lump that grows unusually fast over a few weeks to months
A lump that is hard, fixed to the tissue beneath it, or lies deep under the fascia and cannot be moved
A lump that is very painful without any inflammation
A lump larger than 5 centimeters
A lump with an open sore, bleeding, or skin color change over it
For a suspicious lump, the doctor may order an ultrasound or MRI and take a biopsy first, rather than removing it right away as one would an ordinary lump. In addition, having multiple skin cysts together with bone lumps and intestinal polyps may be a sign of Gardner syndrome, which needs further evaluation.
Why you should not squeeze or puncture a cyst yourself
This is what doctors see most often. Patients tend to squeeze a cyst the way they squeeze a pimple, which is more dangerous than it seems.
Squeezing can rupture the sac wall under the skin, causing inflammation that spreads, with swelling, redness and pain
What many people do not know is that a red, swollen cyst is sometimes inflammation from a ruptured sac, not always an infection, so not every case needs antibiotics. But if it has truly become an abscess, it must be incised and drained.
It leaves scars and dark marks
The sac is still there, so the cyst always comes back in the same spot. Squeezing only pushes out the contents, not the sac wall, and it also causes scar tissue that makes later surgery harder.
Treatment and minor surgery by a doctor
Treatment depends on the type, size, location and degree of inflammation. The approaches a dermatologist uses include:
Observation for a small lump that is not growing, not painful and not bothersome; surgery may not be needed yet
Surgical removal (excision) under local anesthesia is the standard method. For a cyst, the key point is to remove the entire sac wall (complete excision), because if any of the wall is left behind, the cyst will return.
For an inflamed or pus-filled cyst, the doctor usually incises and drains it and calms the inflammation first, then schedules surgery to remove the sac later, about 4 to 6 weeks after the inflammation has settled, because operating during inflammation makes the sac hard to dissect and raises the risk of recurrence.
Biopsy when the appearance is unclear or a malignant tumor is suspected
These minor surgical wounds usually heal well and leave a small scar. Having surgery while the lump is still small and not inflamed gives a smaller wound and a better result than waiting until it has grown or become inflamed.
Frequently asked questions (FAQ)
How does a lipoma differ from a cyst?
A lipoma is soft, movable, painless and has no opening. A cyst is firmer and often has an opening (punctum) at the center; it may contain thick, foul-smelling material and can become inflamed and filled with pus. To tell them apart with certainty, the doctor uses a physical examination or an ultrasound.
Is a lipoma dangerous? Is it cancer?
Most lipomas are not cancer. But if a lump grows fast, is hard and fixed, lies deep, is very painful, or is larger than 5 centimeters, you should see a doctor so that a malignant soft-tissue tumor (sarcoma) can be ruled out with an ultrasound or MRI.
Does an inflamed cyst need antibiotics?
Not always, because some red, swollen cysts result from a ruptured sac wall and inflammation rather than infection. The doctor will assess whether to calm the inflammation, incise and drain the pus, or prescribe antibiotics as appropriate.
Can a lipoma or cyst go away on its own?
Generally no. A lipoma tends to stay the same or slowly grow. A cyst may shrink temporarily but can return as long as the sac wall remains. The way to get rid of it is to surgically remove the whole sac.
Can I squeeze a cyst myself?
No. It risks spreading inflammation, forming an abscess, leaving scars, and the cyst coming back because the sac wall is still there. A doctor should surgically remove the entire sac.
Does lipoma surgery hurt? Is the wound large?
It is done under local anesthesia, so it does not hurt during the procedure. The wound is usually small and heals well, especially when the lump is still small and not inflamed.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed August 3, 2026
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