Sudden Redness and Swelling in One Leg: Causes and What to Know

1. Deep Vein Thrombosis (DVT)
One of the most serious causes is deep vein thrombosis (DVT), which occurs when a blood clot forms in a deep vein, often in the calf or thigh. The clot can block blood flow, leading to swelling, redness, warmth, and pain in the affected leg. DVT is dangerous because the clot can travel to the lungs, causing a pulmonary embolism. Risk factors include long periods of immobility, recent surgery, pregnancy, smoking, obesity, and certain medications. If you notice sudden leg swelling accompanied by pain or shortness of breath, seek medical attention immediately.
2. Cellulitis (Skin Infection)
Cellulitis is a bacterial infection of the skin and underlying tissues. It often develops quickly, causing redness, swelling, warmth, tenderness, and sometimes shiny or tight skin. Blisters or small abscesses may form, and fever, chills, or fatigue can accompany the infection. Cellulitis usually starts when bacteria enter the skin through cuts, scratches, insect bites, or ulcers. Prompt medical treatment with antibiotics is essential to prevent the infection from spreading.
3. Superficial Thrombophlebitis
This condition involves inflammation and clot formation in veins near the surface of the skin. It causes localized pain, redness, and warmth along a visible vein. While generally less dangerous than DVT, superficial thrombophlebitis can occasionally progress to deeper veins, making medical evaluation important
.4. Venous Insufficiency
Chronic venous insufficiency occurs when the leg veins’ valves do not function properly, causing blood to pool. This leads to swelling, redness, heaviness, and sometimes skin changes or ulcers. Unlike DVT or cellulitis, venous insufficiency usually develops gradually but can worsen suddenly in some cases.
5. Other Possible Causes
Less common causes include trauma, allergic reactions, or certain inflammatory conditions. Any sudden or severe swelling should be assessed by a healthcare professional to determine the exact cause and ensure proper treatment.