Dermatofibroma

What a dermatofibroma looks like

• a small, round, firm bump, usually 3 to 10 mm across
• pink, red, tan, brown or darker, often with a lighter center and darker ring
• feels hard and fixed in the skin, like a small button or a lentil under the surface
• often slightly raised, sometimes flat or slightly sunken
• usually single, but some people have several

The dimple sign

When you pinch the skin on either side of a dermatofibroma, it dimples or pulls inward rather than bulging up. This is a useful clue that distinguishes it from many other bumps, although it is not definitive.

Symptoms

Most dermatofibromas cause no symptoms. Some:

• itch
• are tender when pressed or bumped
• catch and bleed when shaving the legs

They usually stay the same size for years, may darken slightly, and rarely disappear completely.

Causes

The exact cause is not certain. Dermatofibromas are thought to be an overgrowth of fibrous tissue in response to minor skin trauma, such as:

• an insect bite
• a splinter or thorn
• a shaving cut
• an ingrown hair or folliculitis

Many people do not remember any injury. People with weakened immune systems, including those with HIV or lupus or on immune-suppressing medicines, sometimes develop many dermatofibromas.

Dermatofibroma vs other skin growths

Dermatofibrosarcoma protuberans

A rare, slow-growing skin cancer called dermatofibrosarcoma protuberans can look like a large dermatofibroma at first. It keeps growing, often over 2 to 3 cm, may become lumpy, and usually appears on the trunk. Any firm bump that continues to enlarge should be biopsied.

Diagnosis

A doctor or dermatologist can usually diagnose a dermatofibroma by looking at and feeling it, including the pinch test. A dermatoscope (magnifying light) typically shows a central white scar-like patch with a fine brown network around it. A biopsy is done if the appearance is unusual, the spot is changing, or melanoma cannot be ruled out.

Treatment

Treatment is not needed for most dermatofibromas because they are harmless. Options if one is bothersome:

• Surgical excision: removing the whole bump with a small margin and stitching the skin. This is the only way to remove it completely, but leaves a scar that may be larger and more noticeable than the original bump, especially on the legs.
• Shave removal: flattens the bump, but it often grows back.
• Cryotherapy: freezing can flatten or lighten it, sometimes leaving a pale mark.
• Steroid injection: may soften or reduce itch in some.

Tips if you shave over one:

• use an electric razor, or shave carefully around the bump
• cover with a small bandage if it gets nicked
• moisturize if it itches

Outlook

Dermatofibromas are benign and do not become cancer. They usually last for many years. If removed with a full excision, they rarely come back. Partial removal often leads to regrowth.

Frequently asked questions

What is a dermatofibroma?

A dermatofibroma is a common, harmless skin bump made of fibrous tissue. It feels firm, like a small button under the skin, and is often pink or brown. It usually appears on the lower legs and may follow a minor injury such as an insect bite.

Are dermatofibromas cancerous?

No. Dermatofibromas are benign and do not turn into cancer. Rarely, a skin cancer can look similar, so any bump that grows quickly, changes color or shape, bleeds or keeps enlarging beyond 2 cm should be checked by a doctor.

How do I get rid of a dermatofibroma?

A dermatologist can remove it surgically, which leaves a scar that may be more noticeable than the bump itself. Shaving or freezing can flatten it, but it often comes back. Since dermatofibromas are harmless, many people choose to leave them alone.

Why does my dermatofibroma itch?

Some dermatofibromas itch or feel tender, especially when rubbed by clothing or shaved over. Moisturizing, avoiding scratching and shaving carefully usually help. A doctor can inject a steroid or remove a persistently itchy one.