Lumps can form under the skin for many reasons, including cysts or swollen lymph nodes. You may want to contact a doctor for an exam if lumps change in size or appearance.

Lumps, bumps, or growths under your skin aren’t uncommon. A lump can form under your skin for many reasons.

Often, lumps are harmless (benign). Specific traits of the lump can sometimes tell you more about possible causes and whether you should contact a medical professional.

Read on to learn more about common causes of hard lumps under your skin and when it’s a good idea to have a lump checked out.

Language matters

You’ll notice that the language used to share stats and other data points is pretty binary, fluctuating between the use of “men” and “women.”

Although we typically avoid language like this, specificity is key when reporting on research participants and clinical findings.

Unfortunately, the studies and specialists referenced in this article didn’t report data on, or include, participants who were transgender, nonbinary, gender nonconforming, genderqueer, agender, or genderless.

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Epidermoid cysts are small, round lumps under your skin. They usually develop when skin cells shed and move into your skin instead of falling off. Epidermoid cysts can also be due to hair follicle damage or a buildup of a protein called “keratin.”

Epidermoid cysts:

  • grow slowly
  • may not go away for years
  • may have a small blackhead in the center of the bump
  • can leak yellow, foul-smelling discharge (keratin)
  • are usually painless but can become red and tender if infected

According to research, these cysts are also twice as common in men and typically don’t develop before puberty.

You can find these cysts anywhere on your body, but you’ll most often see them on your face, neck, or torso.

Learn more about epidermoid cysts.

Lipomas develop when fatty tissue grows under your skin, forming a bulge. These lumps are common and usually harmless. The exact cause of lipomas is unclear, but they may result from physical traumas.

Multiple lipomas can also sometimes be a symptom of an underlying genetic condition such as Gardner’s syndrome.

Lipomas:

  • are most common in adults 40 to 60 years of age
  • are rarely painful
  • grow slowly
  • feel rubbery
  • may seem to move when you touch them

They can appear on any part of your body but most often appear on your shoulders, neck, torso, or armpits.

Learn more about the symptoms and causes of lipomas.

A dermatofibroma is a small, hard bump that grows under your skin. This skin lump is harmless, but it might sometimes itch or hurt.

Although it’s not clear what causes dermatofibromas, some people report having had splinters, insect bites, or other minor trauma at the spot where the lumps develop.

Dermatofibromas:

  • range from dark pink to brown or black, depending on a person’s skin tone
  • have a firm, rubbery feeling
  • according to research, are more common in women
  • tend to be no bigger than 1 centimeter (cm) across
  • grow slowly

You can develop dermatofibromas anywhere, but they often appear on your lower legs and upper arms.

Discover more about dermatofibromas.

Keratoacanthoma (KA) is a small skin tumor that grows out of your skin cells. Sun exposure may play a part in KA development, as it’s more common in high-exposure areas such as your hands or face.

KA may look like a pimple at first but will grow larger over several weeks. The center of the lump can burst, leaving what looks like a crater.

These lumps:

  • may itch or feel painful
  • can grow up to 3 cm in just a few weeks
  • have a core of keratin that may look like a horn or scale in the center of the bump
  • are more common people with light skin and older adults

Learn more about keratoacanthomas (KAs).

A skin abscess is a round, pus-filled lump that develops when bacteria gets underneath your skin’s surface.

Bacterial infections are the most common cause of skin abscesses. Your body reacts to the bacteria by sending white blood cells to the infection site. As tissue around the area dies, a hole forms and pus fills the hole, which causes an abscess.

Abscesses:

  • have a firm membrane surrounding them
  • feel squishy due to pus
  • may be painful
  • may be surrounded by inflamed skin
  • may feel warm to the touch
  • may leak pus from a central pinprick-sized opening

Skin abscesses can develop anywhere on your body.

Learn more about their causes and treatments.

Lymph nodes or lymph glands are small groups of cells located in various parts of the body. The lymph nodes respond to infections by trapping infectious or damaged cells and helping to get rid of them.

As part of the body’s immune response, lymph nodes produce lymphocytes that can cause swelling in the nodes.

Some common reasons lymph nodes may swell include:

  • bacterial infections such as mono or strep throat
  • viral infections including the common cold
  • tooth abscesses
  • cellulitis or other skin infections
  • immune system disorders

You may notice swelling at one or more sites including:

  • under your chin
  • in your groin
  • on either side of your neck
  • in your armpits

Learn more about the causes and symptoms of swollen lymph nodes.

A hernia is a lump that develops when part of your body, such as one of your organs, pushes through the surrounding tissue.

There are several types of hernias. They typically appear in the abdominal area (inguinal hernia), below your chest, or above your hips.

Symptoms of a hernia include:

  • a bulge you can push in
  • pain when you strain the area by coughing, laughing, or lifting something heavy
  • a burning sensation
  • a dull ache
  • the sensation of fullness or heaviness at the hernia site

Discover everything there is to know about hernias.

A ganglion cyst is a small, round, fluid-filled lump that grows under the skin’s surface, usually on your hands. The cyst sits on a small stalk that may seem movable.

It’s not clear what causes ganglion cysts: They’re typically harmless, but irritation to your joints and tendons may play a part.

Ganglion cysts:

  • are often painless but may cause tingling, numbness, or pain if they press on a nerve
  • can grow slowly or quickly
  • appear most often in people between 15 to 40 years of age
  • according to specialists, appear most often in women
  • are usually smaller than 2.5 cm across

These cysts most often develop on wrist joints and tendons, but they can also develop on your palm or fingers.

Learn more about ganglion cysts.

Click through the gallery below to see pictures of the conditions mentioned in this article.

Lumps under the skin are very common and can have a range of causes. In many cases, lumps go away without treatment.

It’s not always possible to tell exactly what causes a lump. If you notice a lump under your skin, keep an eye on it. In general soft, movable lumps are harmless and will likely improve with time.

It’s a good idea to see a healthcare professional if you notice:

  • skin discoloration, swelling, or pain
  • pus or other fluid leaking from the lump
  • tenderness or swelling in the surrounding area
  • changes in color, shape, and size, especially with rapid or steady growth
  • a high fever
  • a lump that’s more than 1 cm across
  • hard or painless lumps that appear suddenly