Most bumps on the leg are harmless. Lipomas, cysts, and dermatofibromas account for the vast majority of lumps people notice, and they rarely need treatment. That said, the feel, location, and behavior of a bump can tell you a lot about what’s causing it, and a small number of lumps do warrant prompt evaluation.
Soft, Movable Bumps
If the bump feels soft and shifts under your skin when you press it, a lipoma is the most likely explanation. Lipomas are slow-growing deposits of fat just beneath the skin, and they account for roughly half of all benign soft tissue masses. They’re most common between ages 40 and 70 and in people who carry extra weight, though they can appear at any age. Lipomas are painless, don’t change color, and can sit unchanged for years. They don’t become cancerous.
Epidermal cysts (sometimes called epidermoid cysts) are another common cause of a movable lump. These dome-shaped bumps range from a few millimeters to about 5 cm across and develop in areas with hair follicles. A telltale feature is a tiny dark dot, called a punctum, at the center of the bump. The cyst contains a buildup of keratin, the same protein that makes up your outer skin layer. They’re usually painless unless they become infected, at which point they turn red, tender, and sometimes drain foul-smelling material.
Small, Firm Bumps Near the Surface
Dermatofibromas are among the most common firm bumps found on the legs, especially the lower legs. They’re typically 0.5 to 1 cm across, feel hard to the touch, and may look brownish or slightly darker than your surrounding skin. A useful self-check: gently pinch the skin on either side of the bump. If it dimples inward rather than popping outward, that’s the classic “dimple sign” strongly associated with dermatofibromas. These bumps are completely benign and often develop after a minor injury like an insect bite or a small cut, though many people don’t remember any triggering event.
Bumps Behind the Knee
A fluid-filled lump at the back of your knee is most likely a Baker’s cyst (also called a popliteal cyst). These form when excess joint fluid pushes into a small pouch behind the knee, often as a result of arthritis, a cartilage tear, or general knee inflammation. Baker’s cysts feel smooth and somewhat squishy, and they may ache or feel tight when you fully bend or extend the knee.
One important distinction: Baker’s cysts can sometimes cause swelling and discoloration in the lower leg that mimics a blood clot. If your calf becomes suddenly swollen, warm, and painful, especially if you haven’t noticed a lump behind the knee, that needs same-day medical evaluation to rule out a deep vein thrombosis.
Bumps Linked to Veins
If you have varicose veins, a new firm or tender lump along one of those veins may be superficial thrombophlebitis, an inflammation of a vein near the skin’s surface. The overlying skin often turns red, feels warm, and may become thick or hard. The vein itself can feel cord-like and sore to the touch. This is common in people with existing varicose veins and is generally not dangerous on its own, but a hard, painful vein that doesn’t improve within a few days should be evaluated to make sure the clot hasn’t extended into deeper veins.
Painful Bumps and Abscesses
A red, warm, rapidly growing bump that’s increasingly tender is often an abscess, a pocket of infection beneath the skin. Abscesses can develop anywhere on the leg but are more common at sites of prior skin damage, such as cuts, shaving nicks, or insect bites. Risk factors include delayed treatment of skin infections, smoking, and being male. Small abscesses sometimes drain on their own, but many need to be opened and drained by a clinician, particularly if the surrounding redness is spreading or you develop a fever.
Bumps on the Foot or Ankle
Ganglion cysts are the most common soft tissue mass in the foot and ankle area. They arise from joint capsules, ligaments, or tendons, often after an injury, and contain a thick, jelly-like fluid. You might notice pain, swelling, or stiffness in the nearby joint. The second most common foot mass is a plantar fibroma, a firm nodule that develops within the thick band of tissue on the sole of your foot. It typically hurts more with walking or standing and sits in the arch area.
Hard Bumps on the Shinbone
A bump that feels like it’s part of the bone itself, rather than sitting in the soft tissue above it, has a different set of causes. A healing stress fracture can produce a hard callus on the tibia that you can feel through the skin. This is especially common in runners and military recruits who recently increased their training load. The area is usually tender to direct pressure.
Rarely, a hard lump on the shinbone can signal a bone tumor. Adamantinoma, for example, is a rare bone cancer that almost always develops in the middle of the tibia or the adjacent calf bone. It tends to cause a lump that’s painful, sometimes swollen and red, and may limit how easily you move the leg. The rarity of this diagnosis is worth emphasizing: the overwhelming majority of shin bumps are from minor trauma or benign bone growths.
When a Bump Needs Evaluation
Soft tissue sarcomas, the cancerous counterpart to benign lumps, are uncommon. They often produce no symptoms early on, which is why size and growth rate matter more than pain. As a general guide, get a bump checked if it:
- Is larger than 5 cm (roughly the size of a golf ball)
- Is growing noticeably over weeks to months
- Feels deep and fixed, meaning it doesn’t move freely under the skin
- Is firm or hard and painless, especially if it appeared without any injury
The first diagnostic step is usually an ultrasound, which can quickly distinguish a fluid-filled cyst from a solid mass. If the ultrasound raises any concern, an MRI provides a more detailed look at the tissue composition and boundaries of the lump. Most people who get imaging for a leg bump walk away with a benign diagnosis, but getting that confirmation is worthwhile when a lump doesn’t fit the typical pattern of a lipoma or cyst.