Lumps and Bumps Under the Skin: When Should You Be Concerned?
Finding a new lump beneath the skin can be worrying. Most soft tissue lumps are benign, but some need monitoring, treatment or further investigation. This guide explains common causes and how ultrasound can help assess a lump safely and quickly.
Why a lump under the skin should be checked
Discovering a lump, swelling, bump or soft tissue mass beneath the skin can understandably cause concern. Many people immediately worry about cancer, but the vast majority of superficial lumps are caused by common benign conditions such as lipomas, cysts, enlarged lymph nodes, bursae, ganglion cysts, inflammation or previous injury.
However, not all lumps behave in the same way. Some can be safely monitored, some may need treatment, and a small number need further assessment to exclude a more serious cause.
What is a soft tissue lump?
A soft tissue lump is an abnormal swelling arising from tissues such as fat, skin, muscle, tendons, ligaments, nerves, blood vessels, lymph nodes or connective tissue. Soft tissue lumps can occur almost anywhere in the body, including the neck, shoulder, back, arms, hands, abdomen, groin, thighs, knees and feet.
Fat and skin
Lipomas and epidermoid cysts are among the most common superficial lumps.
Joints and tendons
Ganglion cysts and bursae often appear near joints, tendon sheaths or pressure points.
Lymph nodes
Nodes may enlarge in response to infection, inflammation or, less commonly, malignancy.
Blood or pus
Haematomas and abscesses may form after trauma, surgery, infection or inflammation.
Nerves
Some lumps arise from nerve sheaths and may cause tingling, numbness or electric-shock sensations.
Soft tissue masses
Most are benign, but suspicious features should be assessed and referred when appropriate.
Why do lumps form?
A lump may form due to abnormal tissue growth, fluid accumulation, inflammation, infection, trauma, enlarged lymph nodes or tumour formation. The underlying cause determines how the lump feels, how it looks on ultrasound and whether it needs monitoring, treatment or further investigation.
| Cause | Example | Typical explanation |
|---|---|---|
| Abnormal tissue growth | Lipoma | A benign fatty growth beneath the skin. |
| Fluid accumulation | Cyst or ganglion | A fluid-filled swelling, often near skin, tendon or joint structures. |
| Inflammation or infection | Abscess or inflamed cyst | May cause pain, redness, warmth and swelling. |
| Trauma | Haematoma | A collection of blood after injury, surgery or anticoagulant medication. |
| Immune response | Reactive lymph node | Nodes can enlarge in response to infection or inflammation. |
Why is ultrasound useful for assessing lumps?
Ultrasound provides detailed information about a lump beneath the skin. It can determine whether the lump is solid or fluid-filled, measure its size, assess blood flow with Colour Doppler and identify whether it arises from or is connected to nearby skin, fat, muscle, tendon, nerve or joint structures.
Ultrasound is safe, non-invasive, radiation-free and performed in real time. It can often reassure patients when a lump has benign appearances and can also identify features that should prompt further investigation.
| Ultrasound question | Why it matters |
|---|---|
| Is it solid or cystic? | This is often the most important first distinction. |
| How large and deep is it? | Accurate measurement helps monitoring and referral decisions. |
| Is there blood flow? | Vascularity may help distinguish inflammatory, benign and suspicious patterns. |
| What tissue does it arise from? | Relationship to skin, fat, muscle, tendon, nerve or joint can guide diagnosis. |
| Are there suspicious features? | Irregular, deep, heterogeneous or vascular masses may need MRI or specialist review. |
Common causes of lumps and bumps under the skin
Lipomas
Lipomas are among the most common soft tissue lumps. They are benign growths made of mature fat cells and often feel soft, rubbery, mobile and painless. They may occur on the back, shoulders, neck, arms or thighs and usually grow slowly.
On ultrasound, a lipoma often appears well-defined with fat-like echotexture, compressibility and minimal vascularity. Many lipomas can be diagnosed confidently using ultrasound when the clinical and imaging features are typical.
Epidermoid cysts
Epidermoid cysts, often called sebaceous cysts, develop when skin cells become trapped beneath the skin surface and continue producing keratin. They may feel round or firm, grow slowly and sometimes show a central punctum. They can become inflamed, infected or painful.
Ultrasound may show a well-defined cystic lesion with internal debris, posterior acoustic enhancement and variable vascularity if inflamed.
Ganglion cysts
Ganglion cysts commonly occur near joints and tendons, especially around the wrist, hand, foot and ankle. They may be related to joint capsule degeneration, tendon sheath irritation or repetitive stress.
On ultrasound, ganglia are usually well-defined fluid-filled structures and may appear connected to a joint or tendon sheath.
Enlarged lymph nodes
Lymph nodes are part of the immune system and may enlarge in response to infection, inflammation, skin conditions or, less commonly, cancer. Ultrasound can assess size, shape, internal architecture and blood flow pattern to help decide whether a lymph node looks reactive or needs further assessment.
Abscesses
An abscess is a collection of pus caused by infection. Symptoms may include pain, redness, swelling, warmth and fever. Ultrasound may show a complex fluid collection, internal debris, surrounding inflammation and peripheral blood flow. It can also help guide drainage procedures when clinically appropriate.
Haematomas
A haematoma is a collection of blood outside the blood vessels, usually after trauma, surgery or anticoagulant medication. Patients may notice bruising, tenderness and swelling. Ultrasound appearance varies depending on the age of the haematoma and can help distinguish it from other soft tissue masses.
Bursae and bursitis
Bursae are fluid-filled sacs that reduce friction. When inflamed, they may produce a localised swelling or lump, commonly around the elbow, knee, hip or shoulder. Ultrasound can show fluid distension, inflammation and surrounding soft tissue changes.
Nerve sheath lesions
Occasionally, a lump may arise from a nerve, such as a schwannoma or neurofibroma. These are often benign but may cause tingling, numbness or electric-shock sensations. Ultrasound can identify whether a lesion is related to a nerve.
Soft tissue sarcoma: rare, but important to consider
Most soft tissue lumps are benign. However, a small number may represent soft tissue sarcoma, a rare cancer arising from connective tissues. The purpose of assessment is not to alarm patients, but to identify the small number of cases that need urgent further investigation.
- Larger than approximately 5 cm
- Increasing in size
- Painful, firm or deep to the fascia
- Recurrent after removal
- Associated with persistent enlarged lymph nodes
- Linked with signs of infection, fever, unexplained weight loss or rapidly worsening symptoms
Most lumps with one or more of these features will still not be cancer. However, further assessment is recommended. Ultrasound can identify suspicious features such as irregular margins, deep location, internal vascularity, heterogeneous appearance or infiltrative characteristics. These may prompt MRI, CT, biopsy or specialist referral.
What happens during a soft tissue ultrasound?
The examination is non-invasive, usually painless and radiation-free. Ultrasound gel is applied to the skin and a high-frequency probe is used to examine the lump and surrounding tissues. Colour Doppler may also be used to assess blood flow.
The scan is usually short, and the findings can help distinguish common benign causes such as cysts, lipomas, enlarged lymph nodes, ganglion cysts, bursitis, haematomas and abscesses from lesions that may need further imaging or referral.
Frequently asked questions
Are most lumps under the skin benign?
Yes. Most superficial lumps are benign and are commonly caused by lipomas, cysts, ganglion cysts, enlarged lymph nodes, bursitis, abscesses or previous injury. However, new, growing or unusual lumps should be assessed.
Can ultrasound show if a lump is a lipoma?
Ultrasound can often identify typical lipoma features such as a well-defined fatty appearance, compressibility and minimal vascularity. If features are atypical, further imaging or referral may be advised.
Can ultrasound tell if a lump is cancer?
Ultrasound can identify benign and suspicious features, but it cannot always confirm cancer. A suspicious lump may require MRI, CT, biopsy or specialist review.
When should I seek urgent assessment?
Seek prompt medical advice if the lump is rapidly growing, larger than around 5 cm, painful, deep, firm, recurrent after removal, associated with infection, or if you have unexplained systemic symptoms.
Final thoughts
Finding a lump under the skin can be worrying, but most soft tissue lumps are benign and caused by common conditions such as lipomas, cysts, enlarged lymph nodes, bursitis, ganglion cysts or previous injury.
Ultrasound is one of the most useful first-line investigations because it can determine whether a lump is solid, cystic, vascular, inflammatory or potentially suspicious. Early assessment can provide reassurance, guide treatment and help identify the small number of cases that need further investigation.
Article preparation and clinical review
This patient information page was prepared with AI-assisted editorial support and reviewed for clinical accuracy by:
- Dr Pedram Aghaei — Vascular Scientist, SVT reg. SVT 679 · Registered Clinical Technologist, RCT reg. 93290 · BMUS 20702
- Dr Hosna Rashidi — BMUS 29386 · SVT reg. M11114
Medical disclaimer: This article is intended for general patient information only and does not replace a medical consultation. If you notice a rapidly growing lump, a lump larger than approximately 5 cm, unexplained weight loss, persistent enlarged lymph nodes, signs of infection or any other concerning symptoms, please seek medical attention promptly.
References used for content preparation: NHS Lipoma; NHS Swollen Glands; NICE NG12 Suspected Cancer Recognition and Referral; British Sarcoma Group Guidelines; BMUS Ultrasound Practice Guidelines; European Society of Musculoskeletal Radiology guidance; American Academy of Orthopaedic Surgeons soft tissue mass resources.
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