Quick Summary
- A dermatofibroma is a firm, benign nodule made of fibrous tissue, most common on the lower legs, often following a minor injury like a bug bite.
- A mole is a cluster of pigment-producing cells and can be flat or raised, brown to black in color.
- The "dimple sign" — the growth dips inward when pinched from the sides — is characteristic of dermatofibromas and doesn't occur with moles.
- Dermatofibromas are typically firmer and more deeply rooted in the skin than most moles, which tend to sit more superficially.
- Both are usually harmless, but any growth that's new, changing, or uncertain deserves a professional look.
A dermatofibroma is one of those common skin growths that quietly confuses people because it can look a lot like a mole at a glance — firm, often brownish, and slow-growing. There's a simple physical exam trick, though, that usually settles the question in seconds.
What a Dermatofibroma Is
A dermatofibroma is a benign growth made of fibrous (scar-like) tissue, thought to sometimes develop in response to a minor skin injury — an insect bite, a small cut, or an ingrown hair — though many appear with no clear trigger at all. They're most common on the lower legs and typically appear as a firm, dome-shaped bump, ranging from skin-colored to brown or reddish-brown. They grow slowly and, once formed, tend to stay stable in size for years. They are entirely benign and are not related to skin cancer risk.
What a Mole Is
A mole (nevus) is a cluster of pigment-producing melanocytes that forms a flat or raised, usually brown, tan, or black spot. Most people have a number of moles that stay stable throughout life, though moles are the category of growth melanoma can arise from, which is why dermatologists recommend watching for change using the ABCDE rule (asymmetry, border irregularity, color variation, diameter over 6mm, evolving appearance).
Key Differences at a Glance
| Feature | Dermatofibroma | Mole |
|---|---|---|
| Made of | Fibrous tissue | Pigment-producing cells |
| Depth | Firm, deeply rooted in the skin | Usually more superficial |
| Common location | Lower legs | Anywhere on the body |
| Dimple sign | Present — dips inward when pinched | Absent |
| Cancer risk | None | Rare, but the category melanoma arises from |
The "Dimple Sign": A Useful Clue
One of the most distinctive features of a dermatofibroma is the "dimple sign" (or Fitzpatrick sign): when the growth is gently pinched from the sides, it dips inward and downward rather than protruding outward, because of how the fibrous tissue is anchored to the deeper skin layers. This doesn't happen with moles. It's a helpful clue, though it's not a substitute for a professional exam if there's any uncertainty.
Have a firm bump you'd like evaluated?
Our board-certified dermatologists see patients at our Burien and Bellevue offices — same-week appointments are often available.
Schedule a Skin CheckWhen to See a Dermatologist
Dermatofibromas don't need treatment unless they're irritated by clothing, itchy, or bothersome cosmetically — they can be removed, though this may leave a scar since they extend into the deeper skin. Any growth that's new, rapidly growing, bleeding, or changing in color or shape should be evaluated to rule out something that needs more than routine observation.