Redness and swelling in the lower legs can stem from a wide range of causes, from poor vein function and fluid buildup to active infection or a blood clot. The most common chronic cause is venous insufficiency, a condition where the valves inside your leg veins stop working properly. But several other conditions, some of them urgent, can produce similar-looking symptoms. Understanding the differences helps you figure out what you’re dealing with and how quickly you need to act.
Chronic Venous Insufficiency
Your leg veins contain a series of one-way valves that open to push blood upward toward your heart and close to prevent it from falling back down toward your feet. When these valves weaken or fail, blood pools in the lower legs, a problem called venous insufficiency. That pooling increases pressure inside the veins, forcing fluid into the surrounding tissue and producing swelling, skin discoloration, and a dull aching heaviness that worsens throughout the day.
Valve failure can happen in the veins just under the skin (superficial veins), in the deeper veins within the muscle, or in the small connector veins between the two systems. Superficial valve failure is often caused by a pre-existing weakness in the vein wall or by excessive stretching from hormonal changes or prolonged standing. Deep vein valve damage usually results from a previous blood clot that scarred the valve leaflets. When the connector veins fail, the high pressure generated by your calf muscles during walking gets redirected backward into the superficial veins, making the problem worse.
The condition progresses through recognized stages. Early on, you might notice spider veins or small varicose veins. As it advances, persistent swelling develops, followed by skin changes: brownish discoloration, dry eczema-like patches, or a thickening and hardening of the skin around the ankles called lipodermatosclerosis. In the most advanced stage, the skin breaks down into open ulcers that are slow to heal. Chronic venous disease is extremely common. A large population study found that nearly 63% of adults showed some degree of venous disease, though many cases remain mild.
Cellulitis: A Skin Infection
Cellulitis is a bacterial infection in the deeper layers of the skin and the tissue just beneath it. It typically produces a spreading area of redness, warmth, pain, and swelling. The redness has a pinkish hue with borders that fade gradually into normal skin rather than forming a sharp line. The skin surface often takes on a dimpled, orange-peel texture. Swollen lymph nodes near the affected area and red streaking up the leg (a sign the infection is traveling through the lymphatic channels) are common with cellulitis and do not occur with blood clots.
The most frequent bacterial culprit is group A streptococcus. The bacteria typically enter through a small break in the skin: a cut, a crack between the toes from athlete’s foot, or even a tiny insect bite. People with chronic swelling in their legs are at higher risk because stretched, fluid-logged skin is more fragile and more easily colonized by bacteria. Cellulitis requires antibiotic treatment and can worsen rapidly if ignored.
Blood Clots in the Deep Veins
A deep vein thrombosis (DVT) occurs when a blood clot forms inside one of the large veins deep within the leg. It typically affects only one leg, causing swelling, tightness, and a deep aching or cramping pain, often in the calf. The skin may look slightly red or flushed, but the redness is usually blanchable (it fades briefly when you press on it) and the skin surface stays smooth, unlike the dimpled texture of cellulitis. The skin temperature is normal or mildly warm.
Several factors raise your risk: being immobile for long stretches (a long flight, bed rest after surgery), active cancer, recent leg injury or casting, and a history of previous clots. Clinicians use a point-based scoring system that adds up risk factors like these. A swollen calf that measures more than 3 centimeters larger than the other leg, pitting edema on only one side, and tenderness along the path of the deep veins all raise suspicion.
DVT becomes dangerous when part of the clot breaks off and travels to the lungs, causing a pulmonary embolism. If you have sudden one-sided leg swelling along with chest pain, difficulty breathing, dizziness, or coughing up blood, that combination is a medical emergency.
Heart Failure and Fluid Overload
When the heart can’t pump blood efficiently, fluid backs up in the body. Gravity pulls that excess fluid downward, so it collects in the legs and feet first. Unlike a blood clot or infection, heart-related swelling almost always affects both legs equally. The swelling is typically “pitting,” meaning that pressing your thumb into the skin leaves a temporary dent. You may also notice shortness of breath, especially when lying flat or during light activity, and your shoes or socks may leave deep impressions by the end of the day.
Other systemic conditions can produce similar bilateral swelling. Kidney disease allows protein to leak out of the blood, reducing the fluid-holding capacity of your bloodstream and letting water seep into tissues. Liver disease does something comparable. In all of these cases, the swelling is a symptom of an underlying organ problem rather than a leg-specific issue.
Lymphedema
Your lymphatic system is a network of tiny vessels that drains excess fluid from tissues and returns it to the bloodstream. When this system is damaged or blocked, protein-rich fluid accumulates in the affected limb, producing a distinctive type of swelling called lymphedema. It differs from venous swelling in an important way: venous edema happens because too much fluid is being pushed into the tissue, while lymphedema happens because the drainage system itself is broken.
Lymphedema develops in stages. In the earliest phase, called Stage 0, the lymph system is already impaired but swelling isn’t visible yet. This latent phase can last months or years. Stage I brings soft, pitting swelling that goes down when you elevate your leg overnight. By Stage II, the swelling no longer resolves with elevation, and the tissue starts to feel firmer as fat deposits and scar-like tissue (fibrosis) develop. Stage III involves severe, persistent swelling with thickened, warty skin changes. Common causes include surgical removal of lymph nodes (often during cancer treatment), radiation therapy, repeated infections, and, in tropical regions, parasitic infections.
How These Conditions Look Different
- One leg vs. both: DVT, cellulitis, and early lymphedema tend to affect one leg. Heart failure, kidney disease, and advanced venous insufficiency usually cause swelling in both.
- Skin texture: Cellulitis creates a dimpled, orange-peel surface. DVT leaves the skin smooth. Long-standing venous insufficiency produces brownish discoloration and hardened skin near the ankles. Late-stage lymphedema thickens and roughens the skin.
- Warmth: A hot, tender area of redness strongly suggests infection. DVT may feel mildly warm or normal. Venous insufficiency and lymphedema are generally not warm to the touch unless an infection has developed on top of them.
- Pain pattern: Cellulitis pain is superficial and tender. DVT pain is deeper, often described as a cramp or tightness in the calf. Venous insufficiency produces a heavy, aching tiredness that worsens with standing and improves with elevation.
- Speed of onset: Cellulitis and DVT develop over hours to days. Venous insufficiency and lymphedema build gradually over weeks, months, or years.
Managing Swelling at Home
For chronic, non-urgent causes like venous insufficiency or stable lymphedema, compression stockings are a frontline tool. They work by applying graduated pressure to the leg, highest at the ankle and decreasing toward the knee, which helps push fluid upward and supports weakened veins. The pressure is measured in millimeters of mercury (mmHg), and the right level depends on severity.
Stockings rated at 15 to 20 mmHg provide mild support and work well for very early swelling or tired, achy legs. A 20 to 30 mmHg stocking is the most commonly recommended range for mild to moderate venous edema. For lower-leg lymphedema or venous insufficiency that doesn’t respond to lighter compression, 30 to 40 mmHg is typical. Stockings above 40 mmHg are reserved for severe cases with significant tissue thickening and are fitted after clinical assessment.
Beyond compression, a few habits make a real difference. Elevating your legs above heart level for 15 to 30 minutes several times a day helps gravity work in your favor. Regular walking activates the calf muscle pump, which squeezes blood upward through the veins. Reducing salt intake limits fluid retention. And keeping the skin well moisturized prevents the small cracks that invite infections like cellulitis, which is especially important if you already have chronic swelling.
Symptoms That Need Immediate Attention
Sudden swelling in one leg, especially if it’s painful and the skin looks pale or feels cool, raises concern for a blood clot and needs same-day medical evaluation. If that swelling comes with chest pain, difficulty breathing, shortness of breath when lying down, dizziness, or coughing blood, call emergency services. These are signs a clot may have reached the lungs.
Rapidly spreading redness with fever, increasing pain, or red streaking up the leg suggests a worsening skin infection that needs prompt antibiotic treatment. And new swelling in both legs, particularly if it comes with shortness of breath or sudden weight gain over a few days, can signal a change in heart or kidney function that warrants urgent evaluation.