Dermatofibroma
Also known as: Fibrous Histiocytoma
Firm, small brown bump - usually on the legs. Harmless. The dimple sign is its signature feature.
What to look for
Side-by-side comparison
Normal skin
No firm bumps
Dermatofibroma
Firm bump, dimple sign
Dermatofibroma is a common, harmless, firm nodule that typically appears on the lower legs of women, though it can occur anywhere. It presents as a small (usually under 1cm), firm, slightly raised, brownish bump that feels like a hard lump under the skin.
The pathognomonic feature is the dimple sign: when the lesion is pinched laterally between two fingers, the center dimples inward rather than protruding outward. This distinguishes it from most other skin nodules.
Dermatofibromas are thought to develop as a reactive process, often after minor trauma such as an insect bite or a small wound. They are completely benign and do not require treatment. They may persist indefinitely or slowly shrink over years.
The clinical importance is distinguishing dermatofibroma from dermatofibrosarcoma protuberans (DFSP) - a rare, slow-growing malignancy that can initially resemble a dermatofibroma. Key differences: DFSP is usually larger (>2cm), tends to grow progressively, and feels fixed to underlying tissue rather than freely mobile.
Quick self-check
Does this look like dermatofibroma? Answer 2 questions.
Does the center dimple inward when you pinch the sides?
Is it a small (under 1cm), firm, brownish bump - most likely on the leg?
Risk factors
- Female sex (more common in women)
- Young to middle-aged adults
- Prior minor skin trauma (insect bites, shaving nicks)
When to see a dermatologist
- ⚠A nodule larger than 1-2cm or growing progressively (may be DFSP)
- ⚠If the dimple sign is absent or the lesion feels fixed to deeper tissue
- ⚠Pain or rapid change in a previously stable lesion
Often confused with
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Full ABCDE check →Frequently asked questions
Do dermatofibromas go away?
They may slowly shrink over years but often persist indefinitely. They are completely harmless and removal is only needed for cosmetic reasons or diagnostic uncertainty.
How is it different from DFSP (cancer)?
Dermatofibroma is small (<1cm), has a positive dimple sign, and stops growing. DFSP is larger (>2cm), progressively grows, feels fixed to tissue, and does not dimple. Any growing nodule larger than 2cm should be evaluated.
Related conditions
Dermatofibrosarcoma Protuberans
Rare slow-growing tumor of the dermis. Looks like a firm plaque or nodule on the trunk - low metastatic potential but high local recurrence.
Common Nevus
Normal moles - clusters of pigment cells. Usually harmless, but monthly monitoring for changes is essential.
Blue Nevus
A blue or blue-black mole caused by deep pigment cells. Stable and benign - but can mimic melanoma.