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uk Health & medical scares sudden one leg swelling • one leg swelling suddenly • calf swelling suddenly • ankle swelling one-sided • leg feels warm and swollen • red or discoloured leg swelling • tight calf sudden swelling • swollen leg after travel • swollen leg after surgery • swollen leg on hormones • swelling in one leg pregnancy • swelling after giving birth leg • possible blood clot in leg • possible dvt symptoms • worried about pulmonary embolism • leg swelling not from injury • one leg bigger than the other • sudden leg oedema • swelling behind knee suddenly

What to do if…
you notice swelling in one leg that appears suddenly

Short answer

If sudden one-sided leg swelling comes with breathlessness or chest pain, call 999 now. If it does not, get same-day urgent assessment using the right UK urgent-care route for where you are.

Do not do these things

  • Do not “wait and see” overnight if the swelling appeared suddenly and is only in one leg.
  • Do not massage or deeply rub the swollen/painful area.
  • Do not do strenuous exercise to “work it out.”
  • Do not take leftover “blood thinners” (or someone else’s medication) to self-treat.
  • Do not drive yourself to A&E if you feel unwell, dizzy, breathless, or have chest pain.

What to do now

  1. Check for emergency warning signs (right now). Call 999 if any are present:
    • new or worsening breathlessness
    • chest pain (including pain worse when breathing in)
    • coughing up blood
    • fainting/collapse or feeling severely unwell
      If you need A&E urgently, do not drive yourself—ask someone to take you or call 999 for an ambulance.
  2. If you do NOT have emergency signs, use the right same-day urgent-care route for where you are:
    • England: use 111 online (age 5+) or call 111.
    • Scotland: call NHS 24 on 111.
    • Wales: call NHS 111 Wales (and use its online tools if you prefer).
    • Northern Ireland: use your GP out-of-hours route (often via your GP practice voicemail/website) or local “Phone First” urgent-care telephone route if your Trust uses it; if you cannot access urgent advice promptly or you’re worsening, go to the nearest Emergency Department. When you speak to someone, say clearly: “sudden swelling in one leg” and whether there is pain, warmth, redness/discolouration, or tenderness.
  3. If you are pregnant or have recently given birth: treat this as same-day urgent—contact your maternity unit/triage (or the urgent-care route above if you cannot reach them quickly).
  4. Make the situation easy to assess (this helps speed care):
    • Note the time it started, how quickly it changed, and whether it’s painful/warm/red.
    • If practical, take 2 photos (front/side) and compare both legs.
    • Write down recent triggers: long travel/immobility, recent surgery/injury, hormone contraception/HRT, previous clots, cancer treatment, recent severe illness.
  5. While you’re waiting for advice/transport:
    • Remove tight socks/garments; keep clothing loose around the area.
    • Avoid vigorous activity and do not massage. If you must wait, avoid being completely still for hours—change position and do gentle ankle/foot movements only if comfortable.
    • Have your medication list, allergies, and (if known) NHS number ready.

What can wait

  • You do not need to figure out the exact cause right now.
  • You do not need to decide about scans, blood tests, or treatment options now—focus on getting assessed urgently.
  • You do not need to contact multiple services at once: 999 if emergency signs, otherwise use the single urgent-care route for your UK nation.

Important reassurance

Sudden swelling in one leg can have harmless causes, but it can also signal a blood clot that needs prompt treatment. Getting assessed quickly is a calm, sensible step.

Scope note

These are first steps to keep you safe and get you to the right urgent assessment. Further decisions should be made with a clinician after examination and (if needed) tests.

Important note

This guide is general information, not a diagnosis. If you feel rapidly worse, develop breathing symptoms or chest pain, or cannot safely get help another way, use emergency services.

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