Subungual Exostosis

Skin and Nail Conditions· Also known as: Dupuytren's exostosis, bony growth under the toenailUpdated Nov 2026

Reviewed by Andrew Schox, BSc(Hons) PGradDipPod MPod, November 2026

At a Glance

Subungual exostosis is a benign (non-cancerous) bony growth that grows from the tip of the end bone of a toe and sits under the nail. It is uncommon, and it is most often found in children and young adults, usually on the big toe. The main problems are pain and a lifted or misshapen nail. Removing the growth with a small operation is the preferred treatment once an X-ray has confirmed it, and most people do well afterwards.

What is it?

Subungual exostosis is a bony growth that comes from the tip of the end bone of a toe, or less often a finger. "Subungual" means under the nail, and "exostosis" means a growth of extra bone. The growth is benign, which means it is not cancer.

The growth is mostly overgrown normal bone, covered by a cap of tough, rubbery tissue (fibrocartilage). It grows slowly, over weeks to months, and as it gets bigger it can push up under the nail and lift it away from the nail bed (the skin the nail sits on).

You may also see it called Dupuytren's exostosis, a bony lump under the toenail or a subungual bone spur. Some experts treat Dupuytren's exostosis as a slightly different condition from the one podiatrists describe.

Who does it affect?

It is uncommon, and no one has a firm figure for how many people have it. It is most often found in children and young adults.

About 75 to 80 per cent of cases are on the top or inner surface of the end bone of the big toe. Other toes can be affected, and fingers less often.

Signs and symptoms

Most people first notice a firm lump under or at the end of the nail that doesn't move. The skin over it is often thick and hard. Over several months there is usually pain (especially when something presses on the nail, such as a shoe), redness, swelling and a nail that looks lifted, bent or misshapen.

As the growth gets bigger, the toe can swell, the skin over it can break down (an ulcer), and the nail bed can become infected.

A few signs can point to something other than a simple exostosis:

A painful nail lump that doesn't change or keeps getting worse despite treatment, or that has unusual features, can mean a different diagnosis, including a cancer such as melanoma.
A dark area under the nail that wasn't caused by an injury can be a sign of melanoma (a type of skin cancer).
A lump that looks like a red, fleshy bump (a pyogenic granuloma) can have an exostosis underneath it. It can also be a skin cancer without dark colour (amelanotic melanoma), which needs a tissue test to rule out.
A sore or wound over the lump that won't heal can mean a nail bed infection, or sometimes a cancer.
A high temperature, skin around the nail that is hot, red, swollen and painful, or pus can mean an infection that may need antibiotics.

These signs don't mean you have any of these conditions. They are the features that make practitioners look more closely.

What causes it?

The cause isn't clear. Most experts think it is a reactive change in the bone, probably after repeated small injuries or ongoing irritation of the tip of the toe. The growth is thought to form when this irritation turns the tissue at the bone tip into the rubbery cap, which then turns to bone.

An earlier toe injury is the best-known link, but it is recorded in only about 30 per cent of cases. Infection, an inherited tendency and a cartilage cyst have also been suggested. Some rarer cases are linked to inherited conditions with many bony growths. Because the cause is uncertain, it isn't something anyone can be blamed for.

How is it diagnosed?

Your podiatrist will look closely at the toe and ask how long the lump has been there, whether it has changed and whether you have had an injury or infection in the toe. They will feel for a firm, fixed lump, check for thick skin at the nail tip, and look for a lifted nail, redness or an ulcer.

An X-ray is the key test. It shows dense bone growing from the end bone of the toe. A sample of tissue may be looked at under a microscope (histology) to rule out other lumps, especially where the diagnosis is unclear or the lump looks unusual.

Exostosis is often missed or mistaken for something else, because it can look like many nail problems. These include:

a wart under the nail, which can look very similar (how the lump responds to treatment, X-ray and tissue tests help tell them apart)
an ingrown toenail
paronychia (an infection of the skin beside the nail)
a fungal nail
a pyogenic granuloma
other lumps under the nail, such as a glomus tumour, a fibroma or a cyst
a nail bed skin cancer or melanoma
much more rarely, a bone or cartilage tumour

Infection or an ulcer can also hide the bony growth underneath. A delay in diagnosis can mean ongoing pain and a more deformed nail.

Treatment

The preferred treatment is a small operation to remove the growth once an X-ray has confirmed it. Most of what is known about treatment comes from case reports and small groups of people, so the evidence is limited.

Looking after it at home

Exostoses rarely go away on their own, and they can grow over time. Not every one needs surgery. When a growth isn't troublesome, it may simply be watched, and the decision about an operation depends on how much it affects your comfort and daily life.

Padding the toe or changing shoes may make it more comfortable. It isn't clear that either one treats the growth itself.

Treatment from your podiatrist

Your podiatrist will examine the toe, arrange or look at an X-ray, and work out whether the lump is an exostosis or something else. They can explain the choice between watching the growth and having it removed. If a lump looks unusual or doesn't settle, they may arrange a biopsy (a small tissue sample) to rule out cancer, including melanoma.

Surgery

Surgery removes the growth along with its rubbery cap. Taking out the whole growth matters, because leaving some behind makes it more likely to come back.

The operation has risks. About 2 in 100 people get an infection, and about 8 in 100 have slower healing of the skin. The growth can return, and the nail may grow back thickened. The nail plate may also be permanently lost or misshapen.

Recovery

The outlook after removal is generally good. After treatment, about 4.0 per cent of people have the growth come back. Changes to the nail (a misshapen or discoloured nail) are the most common complication, affecting about 16.1 per cent.

The growth is more likely to return if it wasn't fully removed, and in people under 18, possibly because their bones are growing quickly, the edge between normal bone and growth is harder to see, and the bone is small. In children and teenagers, missing the diagnosis or treating it the wrong way can lead to harm from too much treatment or from the growth returning.

How long recovery takes isn't clear yet. After surgery, signs that can point to a problem include a growth that returns, pain that is getting worse, or signs of infection such as a high temperature, hot, red, swollen skin or pus. A lump that comes back or looks different from the first one may need more imaging or a tissue test.

Preventing it

Because the cause isn't clear, no way of preventing it has been shown to work. Comfortable shoes that don't rub on the toe may help with comfort, but they haven't been shown to stop an exostosis forming. The best way to lower the chance of it coming back after surgery is complete removal of the growth.

Frequently asked questions

Is a subungual exostosis cancer?

No. It is a benign (non-cancerous) growth of bone. It can look like some skin cancers under the nail, though, which is why unusual or non-healing lumps may need a tissue test to be sure of the diagnosis.

Can it go away on its own?

It rarely does, and it can grow bigger over time. It doesn't always need surgery, though. A growth that isn't bothering you may simply be watched, and the choice depends on how much it affects your comfort and quality of life.

Will my toenail grow back normally after surgery?

Often, but not always. Around 16.1 per cent of people have a misshapen or discoloured nail afterwards. The nail may grow back thickened, and in some people the nail plate is permanently lost or misshapen.

Can children get it?

Yes. It is most often found in children and young adults. In people under 18 it is more likely to come back after surgery, so careful follow-up is important.

Why is it mistaken for a wart or an ingrown toenail?

A thickened lump on the nail, with pain and a lifted nail, looks much like a wart, an ingrown nail or a nail infection. An X-ray shows the bone growth underneath, which is how the difference is usually found.