How to tell if a bump is a cyst? A comprehensive guide

September 28, 2025 •

4 min read

Approximately 1 in every 1,000 people will develop a lipoma, which can be mistaken for a cyst. Understanding the characteristics of different skin growths is crucial to know how to tell if a bump is a cyst and when to seek medical advice.

Quick Summary

A cyst often presents as a slow-growing, movable, and sometimes fluid-filled sac beneath the skin, potentially with a visible dark pore, though specific features vary by type. You can learn to identify key signs and differentiate a cyst from other bumps like lipomas or abscesses by observing texture, mobility, and other symptoms.

Key Points

Cyst vs. Lipoma: A cyst is typically a firm, movable sac containing keratin or fluid, while a lipoma is a soft, fatty lump that moves very easily under the skin.
Infected vs. Non-infected: An uninfected cyst is usually painless, but one that is infected or inflamed becomes red, swollen, and tender.
Never Squeeze: Do not attempt to pop or squeeze a cyst at home, as this increases the risk of infection, scarring, and recurrence.
The Punctum Sign: Common epidermal cysts may have a small, dark pore (punctum) in the center, a distinguishing feature.
When to See a Doctor: Seek medical evaluation for any bump that is painful, rapidly changing, bleeding, or shows signs of infection.
Diagnosis is Key: A physical exam by a doctor is the first step, and imaging like an ultrasound may be used to confirm the nature of the bump.

Understanding the basics of cysts

When you find a new lump or bump on your skin, it's natural to be concerned. Fortunately, many skin growths are benign, or noncancerous, and among the most common is the skin cyst. A cyst is a closed sac that is typically filled with fluid, pus, or other material like keratin. Cysts can appear anywhere on the body and for a variety of reasons, including blocked glands, infections, or injuries. While some cysts might be present at birth, others can develop over time.

Common characteristics of a skin cyst

Most skin cysts, especially the common epidermal inclusion cyst (often called a sebaceous cyst), share a few key characteristics:

Round and dome-shaped: They typically form a symmetrical bump under the skin.
Smooth and movable: They feel smooth to the touch and can often be moved or rolled under the skin with gentle pressure.
Visible punctum: A small, dark pore or blackhead may be visible in the center of the cyst, which is where the keratin and dead skin cells accumulate.
Slow-growing: They tend to grow slowly over time and may fluctuate in size.
Painless (unless infected): A simple cyst is usually not painful. Pain typically only occurs if it becomes inflamed or infected.

When a cyst becomes inflamed or infected

If a cyst ruptures or becomes infected, it can change dramatically. An infected cyst can become:

Red and swollen
Tender or painful to the touch
Warm to the touch
Drain thick, foul-smelling, cheesy material or pus It is crucial to avoid squeezing or popping a cyst, especially if it becomes inflamed or infected. This can push the infection deeper, cause scarring, and often results in the cyst growing back.

How to differentiate a cyst from other bumps

Identifying a bump can be tricky, as several other skin growths share some similar features with cysts. Here’s a comparison to help you tell the difference.

Cyst vs. Lipoma

A lipoma is a benign, fatty lump that grows slowly beneath the skin. The main difference lies in its texture and contents:

Lipoma: Feels soft, doughy, or rubbery to the touch. It moves very easily with slight finger pressure and is composed of fat cells.
Cyst: Is typically firmer and contains fluid or keratin, not fat. It is still movable but might feel more anchored than a lipoma.

Cyst vs. Abscess

An abscess is a painful, pus-filled infection that forms suddenly, whereas an uninfected cyst is typically painless and grows slowly.

Abscess: Red, swollen, painful, and often feels warm to the touch. It contains pus due to a bacterial infection. The fluid from an abscess is also highly contagious.
Cyst: Only exhibits these signs if it becomes infected, otherwise, it is often asymptomatic.

Cyst vs. Pimple (Acne Cyst)

While often confused, acne cysts are different. They form deeper in the skin than a regular pimple but can be tender and inflamed, and unlike a standard cyst, they may not have a central pore.

Recognizing specific types of cysts

Beyond the common epidermal cyst, other types of cysts exist with distinct characteristics.

Ganglion Cysts: These are common, benign cysts that appear near joints or tendons, most often on the wrist or hand. They are filled with a jelly-like fluid and can change in size. While often painless, they can cause nerve pressure leading to pain or weakness.
Pilar Cysts: Also known as trichilemmal cysts, these are a type of epidermoid cyst that primarily forms on the scalp. They are usually firm, smooth, and benign.

When to see a doctor for a bump

While most cysts are harmless, it's always best to have a new or concerning bump evaluated by a medical professional. You should consult a doctor if you notice any of the following:

The bump is growing or changing rapidly.
It is painful, tender, or shows signs of infection like redness and swelling.
The bump is bleeding or seeping fluid.
The lump is hard, immobile, or feels irregular.
You are unsure of the cause and want a definitive diagnosis.

What to expect during diagnosis

Your doctor will likely start with a physical exam of the bump. They will check its size, consistency, and mobility. In many cases, a diagnosis can be made from this exam alone. If there is any doubt, they may use imaging like an ultrasound to see if the lump is solid or fluid-filled. A biopsy, where a tissue sample is removed and tested, may be necessary to rule out more serious conditions like skin cancer.

Comparison Table: Cyst vs. Other Bumps


Characteristic	Cyst	Lipoma	Abscess
Texture	Firm, round sac	Soft, doughy, rubbery	Red, swollen, warm
Mobility	Moves under skin	Moves very easily	Immobile or deep
Pain	Painless unless infected	Rarely painful	Usually very painful
Growth	Slow, can fluctuate	Very slow	Rapid due to infection
Appearance	Skin-colored, with potential punctum	Skin-colored, dome-shaped	Red, inflamed, raised

Treatment options

Treatment for a cyst depends on its nature and whether it's causing issues. For benign, asymptomatic cysts, simple observation may be all that's needed. If a cyst is bothersome, inflamed, or infected, a doctor may suggest:

Drainage: A minor procedure to make a small incision and drain the contents.
Injections: A steroid injection to reduce inflammation.
Surgical Excision: Complete removal of the cyst and its sac to prevent recurrence.

Conclusion

While it can be alarming to find a new bump on your skin, understanding the key features of a cyst can help you determine if it's likely a harmless skin growth or something more serious. Pay close attention to its texture, mobility, and any associated pain or infection. If you are ever unsure, or if the bump is changing, painful, or shows signs of infection, it is always best to seek professional medical advice for an accurate diagnosis and treatment. For more information, read the guide on Epidermoid cysts from Mayo Clinic.

Frequently Asked Questions

Some small cysts can resolve spontaneously, especially with care like a warm compress. However, many persist, grow, or come back if the cyst sac is not fully removed.

An infected cyst will feel warm, tender, swollen, and can be painful to the touch. The skin around it may also appear red.

No, a cyst is a benign sac filled with material, while a tumor is a solid mass. While most cysts are harmless, a doctor might use a biopsy to distinguish a bump from a cancerous tumor.

You should never attempt to pop or squeeze a cyst at home. Doing so can cause pain, increase the risk of infection and scarring, and lead to the cyst returning.

A ganglion cyst is a specific type of fluid-filled sac that forms near joints or tendons, most commonly on the wrist or hand. They are typically painless but can cause discomfort if they press on a nerve.

Cysts can develop for several reasons, including blocked glands or hair follicles, infection, or trauma to the skin. Epidermal cysts often form when surface skin cells are trapped beneath the skin.

If a cyst ruptures, it may drain thick, foul-smelling material. The area can become inflamed, swollen, and tender. You should keep the area clean and see a doctor to prevent infection.