Bump on the side of my foot: possible causes

Finding a bump on the side of your foot can be alarming, especially if it causes discomfort or interferes with daily activities. Most lumps are benign, but some are more concerning. This guide covers the causes of a lump on the side of the foot — the inner or outer edge — and how they’re diagnosed, to help you answer the question, “What is a lump on the side of my foot?” (If your lump is on the sole or arch of your foot rather than the side, see our page on a lump inside the sole, which focuses on plantar fibroma.)

Common causes of a lump on the side of the foot

Ganglion cysts

Ganglion cysts are fluid-filled sacs that develop near joints or tendons. They’re typically soft or firm and can change in size. Most cause no symptoms, but some grow and press on surrounding structures such as tendons or nerves, causing pain.

Most are easily diagnosed with ultrasound; an MRI may be needed if the findings are atypical. Troublesome cysts can be treated with ultrasound-guided aspiration: the skin is numbed, a needle removes the thick fluid, and a small dose of cortisone is injected into the residual sac to discourage recurrence. Some cysts recur and need re-treatment.

Bunionette (tailor’s bunion)

A tailor’s bunion, or bunionette, is a bony prominence on the outer side of the foot, near the base of the fifth toe — often caused by tight or ill-fitting shoes. We try simple treatments first, such as looser shoes and gel pads to protect the area. In more problematic cases, the bunionette can be surgically excised.

Bone spurs 

Bone spurs are bony growths that develop from repetitive stress, arthritis, or abnormal biomechanics. On the side of the foot, they can cause pain or irritation, especially in shoes. A common bony spur at the back of the heel is a Haglund’s deformity, often associated with Achilles tendonitis and bursitis. Treatment usually starts with a gel pad and heel raise to offload the area, anti-inflammatories, and calf strengthening; injections or surgery are reserved for complex cases.

Lipomas

Lipomas are growths of fatty tissue — soft, movable, and usually painless, though they can become bothersome if they press on a nerve or joint. They’re diagnosed clinically and confirmed on ultrasound, and usually need no treatment unless they grow or compress nearby structures.

Plantar fibroma

A plantar fibroma is a benign nodule in the plantar fascia. It’s usually on the sole of the foot, but can occasionally sit near the inner or outer edge of the sole, presenting as a side-of-foot lump. Because the sole is its usual home, we cover the plantar fibroma — its symptoms, imaging, and treatment — in full on our dedicated page: lump inside the sole of the foot.

Tarsal coalition

In younger people, a tarsal coalition — an abnormal connection between two foot bones — can present as a hard lump on the side of the foot, often with pain and stiffness. It’s diagnosed with an X-ray or MRI. We try orthotics and rehab first, with excision reserved for severe or persistent cases.

Accessory navicular syndrome

This occurs when an extra bone near the inner arch becomes prominent and painful. Usually, the extra bone is dormant, but it can flare after an ankle sprain, overuse, or poor footwear. We diagnose an accessory navicular with X-ray, ultrasound, or MRI. Treatment starts with activity modification and orthotics; persistent cases may need an ultrasound-guided injection or surgical excision.

Calluses

Excessive friction on the skin thickens it into a painful lump. Gel pads and orthotics reduce friction, and a podiatrist can trim the thickened skin in troublesome cases.

Dyshidrotic eczema

Dyshidrotic eczema causes small, itchy, fluid-filled bumps, usually on the soles but sometimes on the sides of the feet. The cause is unknown, though it may relate to allergies or stress. Corticosteroid creams and antihistamines often help.

Soft-tissue tumours

Rarely, a benign or malignant soft-tissue tumour can present as a lump on the side of the foot — for example, PVNS or a soft-tissue sarcoma. Early diagnosis matters, and an MRI is the definitive investigation for a suspected tumour.

What is a lump on the side of my foot? How it’s diagnosed

A lump on the side of the foot needs a thorough assessment. Your doctor will ask when the lump appeared, whether it has grown or changed, and whether it is associated with any pain, redness, or swelling — along with your activities, footwear, and any past injury. A careful examination assesses the lump’s size, consistency, mobility, and tenderness, and its location and feel often point to the cause.

Where the diagnosis isn’t clear, investigations may include:

• X-ray — identifies bone causes such as bunionettes, spurs, accessory bones, or tarsal coalitions.

• Ultrasound — visualises soft-tissue lumps such as ganglion cysts or lipomas, and flags whether a lump needs further testing.

• MRI — gives detailed images of bone and soft tissue; the investigation of choice for painful, rapidly growing, or suspicious lumps. A contrast dye is sometimes used.

• Biopsy — performed if there’s any suspicion of a tumour, to confirm the diagnosis.

Frequently asked questions about a lump on the side of the foot

Should I worry about a lump on the side of my foot?

Most are benign — cysts, bony prominences, or fatty lumps. But see a doctor promptly if the lump is rapidly growing, painful, hard and fixed, or associated with skin changes, as these features need to be evaluated to rule out something more serious.

What is the hard lump on the outer side of my foot?

Common causes on the outer edge include a bunionette (near the base of the little toe), a bone spur, or a ganglion cyst. A firm, fixed lump in a younger person can be a tarsal coalition. An examination and imaging tell them apart.

Is a lump on the side of my foot the same as one on the sole?

Not usually. A lump on the sole or arch is most often a plantar fibroma, which is a different condition from the bony and cystic lumps that appear on the side of the foot.

Do lumps on the side of the foot need surgery?

Often not. Many settle with changes in footwear, padding, or orthotics, and cysts can be aspirated. Surgery is reserved for lumps that remain painful, continue to grow, or don’t respond to simpler measures.

When should I see a doctor about a foot lump?

If it’s painful, growing, hard and immovable, changing in appearance, or affecting how you walk. An accurate diagnosis is the key to the right treatment.

Final word from Sport Doctor London on a lump on the side of my foot

A bump on the side of your foot can have many causes, ranging from benign cysts to bony or structural problems. An accurate diagnosis is key to effective treatment, so see a sports doctor if you’re concerned — particularly if the lump is growing rapidly or causing pain.

To book a foot assessment with Dr Masci in London, contact the team here or call +44 (0) 203 488 0350.

Related conditions:

• Lump inside the sole of the foot (plantar fibroma)
• Ganglion cysts
• Haglund’s deformity and Achilles bursitis
• Accessory navicular syndrome
• Tarsal coalition
• PVNS (pigmented villonodular synovitis)

Click on the site of your lump on the side of your foot to identify possible causes