Swollen Legs - Causes

It would be a very difficult task to list all possible causes of swollen legs. Some are listed, and briefly discussed below. Many are linked to individual leaflets with more information about that specific condition. They are divided into those which tend to affect one leg or one part of a leg, and those which tend to affect both, but some conditions can cause either.

What are the causes of swelling of both legs?

The most common cause of swelling in both legs is oedema. This is a collection of fluid in between the cells, which are the building blocks of the tissues of our body. Oedema can occur in one particular part of the body, or it can be generalised. If generalised, gravity takes the fluid to the part of you which is hanging down. For most people, this is their legs. This type of oedema tends to improve at night when you have your legs up. See the separate leaflet called Oedema (Swelling).

Causes of oedema affecting both legs symmetrically include:

  • Heat. Some people will find their legs swell up a little in hot weather. Usually this is nothing to worry about and does not need treatment.
  • Long journeys. If your legs are hanging down and not moving for long periods of time, you can develop swollen legs. This improves once you are walking about again, or once you lie down at night. This happens because your muscles are not working to move the blood in your blood vessels around. This means the blood pools in the bits of you which are hanging down, putting pressure on the blood vessels and forcing fluid out into the spaces between them. To avoid this, get up and walk around regularly if possible. If not, move your feet and legs around as much as you can.
  • Pregnancy. Pregnant women may have swollen legs in late pregnancy. Usually this is par for the course and nothing to worry about, but if you are pregnant, your midwife will be doing regular checks to be sure you don't have a blood pressure problem (pre-eclampsia) causing it.
  • Heart failure. If you have this condition, your heart is not working as effectively to push the blood around your circulation. You may also feel out of breath, and this can be worse when lying down flat at night or on walking.
  • Anaemia. This is a problem with the red blood cells of your body.
  • Kidney diseases such as nephrotic syndrome, acute kidney injury and chronic kidney disease.
  • Conditions where there are low levels of protein. If there are low levels of protein in the blood, less fluid is drawn into the blood from the surrounding areas. Conditions causing low protein levels include malnutrition, nephrotic syndrome, liver failure, and a gut condition called protein-losing enteropathy.
  • Side-effects of medicines such as calcium-channel blockers.
  • Having very low thyroid levels (hypothyroidism). This is normally accompanied by other symptoms such as tiredness and gaining weight.
  • Idiopathic oedema. This means there is oedema but no specific cause has been found for it.

What are the causes of swelling affecting one leg or part of one leg?

There are numerous causes including:

  • Injuries - for example, fractures, sprains, large bruises.
  • Wear and tear arthritis (osteoarthritis) - in particular this might affect a knee (or both knees) or the big toe(s).
  • Joint problems caused by inflammation - for example, gout, rheumatoid arthritis, psoriatic arthritis. One or more joints would be warm, red and painful.
  • Skin infections - for example collections of pus (abscesses) or cellulitis.
  • Skin reactions - for example an allergy to a bite or sting or medicine.
  • Deep vein thrombosis (DVT). This is a blood clot in the deep blood vessels, which most commonly affects the calf. You are more at risk of a DVT if you have recently had a period of time when you didn't move very much. Examples include a long plane journey, an illness, an operation.
  • Bone infection (osteomyelitis).
  • Lymphoedema. In this condition lymph fluid collects in the tissues because it can't drain very well. This is usually because the lymph nodes are blocked for some reason. This can happen after an operation, after radiotherapy, or due to cancer, injury or infection.
  • Baker's cyst. This is a soft swelling at the back of your knee.

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Dr Mary Harding
Peer Reviewer:
Dr Laurence Knott
Document ID:
29430 (v1)
Last Checked:
04 July 2017
Next Review:
03 July 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.