6. Blood Clot (Deep Vein Thrombosis) — The Emergency
The one that can’t wait.
A DVT almost always affects one leg only. That asymmetry is the single most important clue on this entire page.
What it looks like:
- Sudden swelling in one leg
- Pain or tenderness, often in the calf — sometimes described as a cramp that won’t release
- Warmth in the area
- Redness or a bluish tinge
Why it’s urgent: the clot can break free and travel to the lungs — a pulmonary embolism, which can be fatal. If leg swelling comes with sudden shortness of breath, chest pain that worsens when you breathe in, coughing blood, a racing heart, or fainting, call emergency services immediately.
Risk rises with recent surgery, long immobility or long flights, cancer, pregnancy and the weeks after delivery, estrogen-containing medications, and previous clots.
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Both legs swelling gradually over months is very unlikely to be a clot. One leg swelling suddenly is exactly what one looks like.
7. Medications
Covered on the first page, and worth repeating because it’s so frequently the answer: calcium channel blockers (especially amlodipine), NSAIDs, steroids, hormone therapy, pioglitazone, gabapentin and pregabalin.
Never stop a prescribed medication on your own — but do raise it, because there’s often a straightforward adjustment.
8. Sitting, Standing, and Gravity
Sometimes it really is the boring explanation.
Long flights, long drives, desk jobs, and jobs spent on your feet all let fluid pool in the lower legs, because the calf muscles — which normally pump blood back up — aren’t being used. Hot weather makes it worse by widening blood vessels.
How to tell it’s this: both legs, mild, comes on through the day, gone by morning, no pain, no skin changes, no breathlessness. It responds well to walking, elevating your legs, and moving regularly.
