A dermatofibroma is a small, firm, benign skin growth that most often appears on the legs, arms, or other extremities. These bumps are typically between 5 and 10 millimeters across, feel like a hard pea under the skin, and are completely harmless. They’re one of the most common benign skin lesions, showing up most frequently in adults between the ages of 20 and 50, with women affected roughly twice as often as men.
What a Dermatofibroma Looks and Feels Like
Dermatofibromas present as round, slightly raised bumps that feel noticeably firm or hard when you press on them. The color varies depending on skin tone, ranging from pink or reddish-brown to dark brown. Some have a slightly darker ring around the edges. The surface may feel smooth or slightly rough, and the growth sits partly within the deeper layers of skin, so it can feel like there’s a small button embedded beneath the surface.
Most people develop a single dermatofibroma, though having two or three at different times isn’t unusual. The legs are the most common location, particularly the lower legs, but they can appear on the arms, torso, or anywhere on the body. They grow slowly, usually reaching their full size within a few months, and then stay unchanged for years or even permanently.
The Dimple Sign
One of the easiest ways to recognize a dermatofibroma at home is the “dimple sign.” If you pinch the skin around the bump from the sides, the center dimples inward rather than popping outward. This happens because the growth is tethered to the deeper layers of skin. Most other small bumps, like cysts or moles, push outward when squeezed. The dimple sign isn’t a formal diagnosis, but it’s a reliable clue that what you’re looking at is a dermatofibroma rather than something else.
What Causes Them
The exact cause isn’t fully understood, but dermatofibromas are thought to be an overgrowth of fibrous tissue in the skin, likely triggered by minor injury. Insect bites, splinters, small cuts, or other minor skin trauma may set off the process. The body responds by producing an excessive amount of fibrous cells (called fibrocytes) in the middle layer of skin, creating a dense knot of tissue that hardens into the bump you feel. Under a microscope, the lesion shows spindle-shaped cells arranged in bundles, mixed with collagen fibers. A hallmark finding is “collagen trapping,” where the growing cells wrap around individual collagen bundles at the edges of the lesion.
They are not cancerous, not contagious, and not caused by infection. There’s no clear genetic link for isolated dermatofibromas, and most people who develop one are otherwise completely healthy.
When Multiple Dermatofibromas Appear at Once
Developing many dermatofibromas over a short period, sometimes called multiple eruptive dermatofibromas, is rare and worth paying attention to. In a review of 72 reported cases, about 70% of patients with this pattern had an underlying condition, most commonly related to immune suppression. Autoimmune diseases, blood cancers, and immunosuppressive medications have all been linked to sudden crops of these bumps. The leading theory is that dermatofibromas represent a type of immune reaction in the skin, and when the immune system is suppressed, it can’t properly control the process, leading to many lesions at once. That said, roughly 30% of people with multiple eruptive dermatofibromas had no identifiable underlying cause.
How Dermatofibromas Are Diagnosed
Most dermatofibromas can be identified by their appearance and the dimple sign alone. When a dermatologist examines a questionable bump with a dermatoscope (a magnifying tool with a light), dermatofibromas show a characteristic pattern: a white, scar-like area in the center surrounded by a delicate network of pigment at the edges. This pattern is distinctive enough to rule out most other growths without a biopsy.
A biopsy may be recommended if the growth looks unusual, is rapidly changing, or needs to be distinguished from a rare skin cancer called dermatofibrosarcoma protuberans (DFSP). Despite the similar name, DFSP is a locally invasive soft tissue tumor that behaves very differently. Under the microscope, the two look distinct: dermatofibromas have varied cell shapes and sizes with sclerotic (scarred) areas, while DFSP cells are uniform in appearance and tend to invade into the fat layer beneath the skin. Special staining techniques can further distinguish them, though appearance alone is usually sufficient for an experienced pathologist.
Treatment Options
Most dermatofibromas don’t need treatment. They’re benign, stable, and pose no health risk. Many people choose to leave them alone once they have a diagnosis. The most common reasons people seek removal are cosmetic concerns, discomfort from clothing rubbing against the bump, or persistent itching or tenderness.
Surgical excision is the most definitive option. Because dermatofibromas extend into the deeper layers of skin, removal requires cutting below the surface, which typically leaves a scar. For many people, the scar ends up being more noticeable than the original bump, so this tradeoff is worth considering. If excision doesn’t extend deep enough, there’s a chance of recurrence. For a common variant called cellular dermatofibroma, recurrence rates were historically reported at 26% to 50%, though more recent data suggests the rate is closer to 10% when margins are involved on the initial biopsy.
Cryotherapy (freezing) and steroid injections can flatten or shrink a dermatofibroma, but they often don’t eliminate it completely and may cause changes in skin color at the treatment site. Laser treatments, including carbon dioxide laser, have shown some success. In case reports, patients have experienced complete flattening of the bump with no recurrence at seven to eight months of follow-up, though mild discoloration around the treated area is a common side effect.
What to Expect Long Term
A dermatofibroma that’s been confirmed as benign will almost certainly stay benign. These growths do not transform into cancer. They may shrink slightly over many years, but most persist indefinitely. Some people notice occasional mild itching or tenderness, particularly if the bump is in a spot that gets bumped or rubbed frequently. If a previously stable dermatofibroma begins growing rapidly, changes color dramatically, or starts bleeding without injury, those changes warrant a closer look to make sure the original diagnosis was correct.