Quick answer
A subungual exostosis is a small benign bone growth from the tip of the toe (the distal phalanx) that pushes upward under the toenail. It is most common on the great toe in adolescents and young adults. The classic story: a painful, persistent “ingrown toenail” or “wart under the nail” that does not respond to standard treatment for months — until an X-ray shows the underlying bone growth. Surgical removal cures it in nearly all cases, with low recurrence.
What it is
The bones of the toe (phalanges) normally have a smooth dorsal surface where the nail bed sits. In subungual exostosis, an outgrowth of bone forms on this dorsal surface, often capped with a layer of cartilage. As it grows, it lifts the nail upward and pushes against the soft tissue under the nail, causing pain, deformity, and sometimes ulceration of the overlying skin.
The condition is named after Dupuytren, who described it in 1847. Despite being known for nearly two centuries, it remains commonly misdiagnosed — most often as a stubborn ingrown toenail, plantar wart, or chronic infection.
Causes
The exact trigger is unclear, but prior trauma to the toe is the most consistent association — especially in adolescents and young adults. Theories include:
- A small fracture or stress injury that heals with abnormal bone formation
- A reactive bony response to chronic local inflammation
- Possible genetic predisposition in some families
Most cases are isolated and not associated with broader bone or joint disorders.
Symptoms
- A firm, immovable lump under or beside the toenail — pressure on it feels like pressing on bone, not soft tissue
- Pain with shoe pressure or direct contact with the lump
- Nail deformity — the nail is lifted, distorted, or grows abnormally over the lump
- Erythema and swelling of the overlying skin
- Skin breakdown or ulceration in advanced cases as the lump erodes through the soft tissue
- Often a long history of being treated for “ingrown toenail” or “wart” without improvement
Diagnosis
- History and exam — a hard, fixed, firmly attached bump under the toenail in a young adult or adolescent strongly suggests the diagnosis
- Lateral X-ray of the affected toe — the key test; shows the bony outgrowth from the dorsal phalanx
- Multiple X-ray views sometimes needed if the growth is small or oriented obliquely
- MRI rarely needed but can characterize the cartilage cap if the bony lesion is unusual
- Pathology — the removed tissue is examined to confirm benign nature
Treatment
Surgery
Subungual exostosis does not respond to medications, soaks, or topical treatments. The bone growth must be removed surgically.
- Procedure: under local anesthesia (digital block), the surgeon removes a portion of the overlying nail to access the growth, removes the bony outgrowth and any cartilage cap, and contours the bone underneath
- Setting: typically in-office or outpatient surgery; takes 20 to 40 minutes
- Recovery: the toe is bandaged for 2 to 4 weeks; comfortable shoes throughout; back to most activities within 1 to 2 weeks; running and impact sports usually delayed 4 to 6 weeks
- The nail that was partially removed grows back over 6 to 12 months
What to expect
- Pain relief is usually rapid and dramatic once the growth is removed
- Recurrence rate is low (under 10%) when the entire growth is excised
- The nail may grow back somewhat differently than before (slight ridging, mild deformity) but usually cosmetically acceptable
- Confirmatory pathology rules out the very rare malignant lesions that can mimic exostosis
When the diagnosis is uncertain
If imaging shows an atypical growth or pathology raises any concern for malignancy, referral to an orthopedic oncologist for further evaluation is appropriate. The vast majority of subungual exostoses are entirely benign.
When to see a clinician
- A persistent painful bump under a toenail that has not responded to several weeks of standard ingrown-nail care
- A toenail being visibly lifted or deformed by something underneath
- A “wart” under a nail that does not respond to wart treatments
- Recurring localized infection at the same toe nail edge
- Skin breakdown or ulceration over a hard lump near a toenail
Bottom line
Subungual exostosis is a benign bone growth under the toenail that can resemble a stubborn ingrown toenail or wart. A lateral X-ray of the toe is diagnostic in most cases. The treatment is straightforward outpatient surgery to remove the bony growth, with low recurrence. Persistent symptoms in the same toe nail edge despite standard care are a reason to seek further evaluation.
Frequently asked questions
What does a subungual exostosis feel like?
A firm, hard bump under or beside the toenail that does not move when pressed (unlike a soft tissue lump). It often pushes the nail upward or distorts its shape. Pain is common with shoe pressure or direct contact, but the lump can be painless until it grows large enough to interfere with the nail. Many patients are told they have a stubborn ingrown toenail or a wart for months before the underlying bone growth is recognized.
How is subungual exostosis different from an ingrown toenail?
An ingrown toenail is the nail edge digging into soft skin; the problem is the nail itself, and the lump is fleshy and inflamed. Subungual exostosis is a bone growth pushing up from below; the lump is firm and bony, and the nail is being deformed by something underneath. Standard ingrown-nail care (soaks, antibiotic ointment, lifting the nail edge) helps an ingrown but does nothing for an exostosis. When a 'stubborn ingrown' is not improving after a few weeks of proper care, an X-ray can be a useful consideration to rule out subungual exostosis.
How is subungual exostosis diagnosed?
X-ray is the key test. A lateral X-ray of the affected toe shows the bony outgrowth from the dorsal surface of the distal phalanx (tip of the toe bone). The diagnosis is usually obvious once imaging is done. Sometimes the X-ray is initially read as normal because the growth is small or the angle is suboptimal — if the clinical picture fits and the first X-ray is unrevealing, repeat or different views often show it.
Does subungual exostosis need surgery?
Yes, in nearly all symptomatic cases. There is no medication or topical treatment that shrinks the bony growth. The standard treatment is a small in-office or outpatient surgical excision under local anesthesia, removing the bone growth and contouring the area. A portion of nail may need to be temporarily removed for access. Recurrence is uncommon when the entire growth is removed.
Is subungual exostosis cancerous?
No. Subungual exostosis is a benign bony outgrowth, not cancer. It is sometimes confused on imaging with osteochondroma (also benign) or, very rarely, with malignant bone tumors. A pathologist examines the removed tissue to confirm benign nature in any uncertain case. The vast majority are entirely benign and the surgery is curative.
Sources
Last updated: May 3, 2026
About the author
Written and reviewed by a Doctor of Podiatric Medicine (DPM) practicing in Arizona for 6+ years. Board-certified by the American Board of Podiatric Medicine (ABPM); graduate of Midwestern University Arizona College of Podiatric Medicine.
Last clinically reviewed: May 3, 2026