Hard Lump Under Skin on Leg: Causes & What to Do

A firm, mobile subcutaneous lump on the leg has a broad differential. Common causes:

• Lipoma: Benign fatty tumor; soft, doughy, mobile. Most common.
• Epidermoid/Sebaceous Cyst: Keratin-filled sac; central punctum; may inflame/infect.
• Ganglion Cyst: Joint/tendon sheath fluid; often near knee/ankle; fluctuant.
• Fibroma: Firm, fibrous benign tumor.
• Enlarged Lymph Node: Inguinal nodes react to lower limb infection/inflammation; firm, mobile.
• Varicose Vein: Dilated, tortuous vein; bluish; may feel like a lump.
• Baker's Cyst: Popliteal fossa swelling from knee effusion (arthritis, meniscal tear).
• Hernia: Inguinal/femoral hernia extending to thigh.
• Sarcoma (Rare): Deep, fixed, rapidly growing; urgent referral needed.

When to See a Doctor

• Lump >2 cm, growing, fixed, painful, or associated with skin changes.
• History of cancer.
• Systemic symptoms (fever, weight loss).

Ultrasound is usually the first imaging test. Biopsy if malignancy suspected.