Sudden redness, warmth, or swelling in one leg can signal serious health problems that require immediate attention.

One major risk is deep vein thrombosis (DVT), where “a blood clot forms in a deep vein, usually in the leg.” If the clot breaks free, it can cause a life-threatening pulmonary embolism.

Another possibility is cellulitis, “a bacterial skin infection” that spreads quickly and usually requires antibiotics. Superficial thrombophlebitis may also be the cause, when “a clot forms in a vein closer to the skin,” leading to pain and tenderness. Though often less dangerous than DVT, it still needs medical care.

Chronic venous insufficiency can also cause swelling and redness, as faulty vein valves lead to blood pooling, skin changes, or even ulcers. Other causes include gout, arthritis, lymphedema, or injury.

Doctors warn to seek urgent help if swelling is sudden, painful, or comes with fever, chills, chest pain, or shortness of breath, since these could signal a pulmonary embolism. Acting quickly is key to preventing serious complications.

Disclaimer: This information is for educational purposes only and not a substitute for professional medical advice.