When you notice swelling in both legs/feet (bilateral), often the causes are different than that of swelling noted in one leg (unilateral). In addition, these causes tend to be more widespread - such as a result of systemic illness. If you notice swelling in both of your legs or feet that either 1. doesn't get better in the course of a day or two, 2. is accompanied by new pain, or 3. Seems to steadily worsen over time - it's time to see your doctor!
Here are some of the causes of bilateral leg swelling:
1. Venous insufficiency: Many people would refer to this as "bad circulation." The word "venous" refers to the veins in the legs. These veins are responsible for carrying fluid/blood back to the heart to be re-oxygenated. With increased age and also in those whose lifestyle involves a lot of standing, the valves in veins that help propel blood upwards can stop functioning. Prolonged standing can predispose people to swelling because gravity causes pooling of blood and fluid in the legs that is harder to overcome over time. At its worst, venous insufficiency can cause ulcerations of the skin (think of a really thin, over-filled water balloon that eventually bursts open). Don't put off having this examined!
2. Heart Failure: The heart is the core of circulation in the body. Therefore, it only makes sense that if the heart is not adequately pumping blood from the arms/legs and back into circulation, fluid will accumulate in the legs. Whether you are aware of underlying heart failure or not, your leg swelling should be addressed to prevent further complications down the line.
3. Kidney Disease: The kidneys serve a few very important functions. If the kidneys are not functioning normally, proteins normally holding fluid in the vascular system can be low, causing fluid to enter into the space outside of this system. Kidney disease often occurs with uncontrolled diabetes.
4. Liver Failure: Liver failure's link to swelling in the legs and feet is protein, similarly to kidney disease. Liver failure can be caused by Hepatitis, alcoholism, and immune system disorders.
5. Lymphedema: Lymphedema is a condition in which the lymph system has blockages which cause fluids that normally circulate throughout the body to settle into the tissues in legs and feet. Lymphedema can be hereditary. Tumors and infections can also be the cause of blocked lymph channels.
6. Pregnancy: Pregnancy changes a lot of things within a woman's body. Swelling can be due to changes in hormone levels from the pregnancy. In addition, swelling in the legs can occur as the baby grows, as it can place pressure on the large veins in the pelvis, slowing blood flow back to the heart.
7. Injury or blood clot: ... or really any condition which normally causes swelling in ONE leg can occasionally occur in both. Injury-wise, if you fall from a height or are in a car accident, injuries may be present on both sides causing swelling. Blood clots can occur in two leg veins at the same time, but they can also occur higher up in the circulatory system causing swelling to be present in both legs. Gout and other types of arthritis may be more often seen in one leg at a time - however, there are some instances when a person may have high enough levels of uric acid that it deposits in both sides for instance.
If you have swelling in both legs that you did not notice before, make an appointment with your doctor for evaluation. It may be a minor cause that is easily remedied (in which case you get better faster) or it could be a serious medical condition that needs immediate and thorough attention!