Edema

Edema is commonly called "swelling" or "puffiness" in everyday language. It refers to an increase in fluid outside the blood vessels, in the tissue spaces between cells and capillaries—the interstitium. Common everyday experiences include "my face is puffy in the morning," "my legs feel swollen and achy in the evening," or "my rings and shoes feel tight."

Edema usually appears relatively evenly over a broad area, such as the legs, which are affected by gravity, rather than in just one spot. Localized swelling accompanied by pain or localized warmth is described separately below as localized swelling, or tumefaction. For whether pressing with a finger leaves an indentation, see Pitting edema.

Fluid movement between blood vessels and tissues depends on the balance between two forces. One is the blood pressure inside the capillaries, or hydrostatic pressure, which pushes fluid out of the vessels. The other is the osmotic pressure created by proteins in the blood, which draws fluid into the vessels. When this balance tips to one side, more fluid than usual remains between the tissues. You can read more about this in Starling forces.

Some of the fluid that enters the tissue spaces returns through the veins, while the rest returns through the lymph vessels. The lymphatic system has no pump like the heart, so muscle contractions squeeze the lymphatic vessels to propel fluid along. Pressure changes in the chest during breathing and contractions of the lymphatic vessel walls also help circulation.

Prolonged standing or sitting therefore means that venous blood and lymph must travel against gravity for longer, allowing more fluid to collect in the legs toward the end of the day.

• Swollen legs in the evening — This is common after standing or sitting all day, or keeping your legs below heart level for a long time. You may also readily notice a feeling of swelling in hot weather or after a long flight.
• A puffy face in the morning — Because the body barely moves during sleep, fluid remains around the face, then gradually subsides as you get up and move around.
• The day after eating salty food — A high-sodium meal makes the body retain more water, so you may feel more swollen than usual.
• Before menstruation — Changes in the body's fluid balance during the menstrual cycle may increase the feeling of swelling. See Premenstrual edema.
• During pregnancy — Increased body fluid and the enlarged uterus affecting blood flow in the lower body make the legs more prone to swelling. See Fluid retention and edema during pregnancy.

When the calf muscles move, they act as a pump that pushes venous blood and lymph upward. This is why the calves are often called the "second heart." When swelling builds up, getting this muscle pump moving again is a basic step.

• Get up about once an hour to walk or move gently.
• Even while seated, try the ankle pump mechanism by raising and lowering your toes.
• In the evening, lie down and rest your legs on a pillow or cushion.
• Try reducing your usual intake of salty foods and broth.
• Eating a large amount of food and drinking alcohol just before bed can increase facial puffiness.
• Rather than cutting back too much on water, drinking enough in response to thirst is better for the body's balance. See also Fluid balance and edema.

Movement, compression, and elevation are three approaches often discussed together when managing everyday swelling.

The underlying physiology is the calf's skeletal muscle pump. When the calf muscles—the gastrocnemius and soleus—contract, they compress the veins running between them, pushing blood upward through the valves. When the muscles relax, the valves close to prevent blood from flowing backward. During prolonged standing or sitting, this pump cannot operate regularly, so blood pools in the lower legs and fluid leaks from the capillaries into the tissues.

• Movement — This is the most basic way to reactivate the pump. Get up and walk about once an hour, or use the ankle pump mechanism while seated. Experimental findings have also shown reduced calf swelling simply from frequently interrupting time spent sitting.
• Compression — Compression stockings or compression socks apply gentle pressure to the surface of the legs, helping the veins move blood upward. When choosing them for the first time, take accurate measurements to select the right size. Putting them on after getting up in the morning, before swelling develops, can be more comfortable.
• Elevation — Raising the legs above heart level allows gravity to work in favor of venous and lymphatic return. See Leg elevation for how to do this.

The key is not the type of posture, but how long you maintain one posture without interruption. Whether standing or sitting, moving from time to time helps reduce swelling.

These terms classify swelling by its characteristics. They describe what the swelling is like rather than why it occurs.

The most common criterion is reversibility. Swelling that develops after prolonged standing or sitting and clearly decreases after resting with the legs elevated or sleeping overnight is described as reversible. Swelling that does not readily subside over time, or that seems to involve changes in the texture of the skin and subcutaneous tissue, is relatively closer to irreversible. The second criterion is whether pressing leaves an indentation, and the third is whether it is temporary swelling that develops and subsides within a day or two, or swelling that recurs and persists over a long period.

Lymphedema is a representative condition involving persistent swelling. It is a chronic condition addressed by complete decongestive therapy, and differs in nature from ordinary swelling that appears in the evening and then subsides.

Venous edema

This swelling occurs when the upward return of blood through the veins slows, increasing venous pressure in the legs. It becomes more noticeable toward evening and may be more pronounced in people with varicose veins.

Idiopathic edema

This term describes swelling for which a single clear cause is not readily identifiable. "Idiopathic" does not mean there is no cause; rather, it means the name itself does not specify a cause. The skin may appear taut, or an indentation may remain after pressure is applied.

When blood protein levels, especially albumin, decrease, oncotic pressure—the force that draws water into the blood vessels—weakens. More water then moves out of the vessels into the tissues. This concept is also searched for as "hypoalbuminemia and edema."

Starling forces describe how the balance between hydrostatic pressure and oncotic pressure inside and outside blood vessels determines the direction of water movement. Hydrostatic pressure is the force with which blood pushes toward the tissues, while oncotic pressure is the force with which proteins draw water into the vessels. When plasma protein levels fall, this pulling force weakens, leaving more water in the tissues.

This differs in mechanism from evening leg swelling caused by increased venous pressure in the legs. Because it results from a reduction in the proteins in the blood itself, swelling can appear in multiple parts of the body, not just the legs. It is not a change that occurs immediately simply because you eat a little less protein in your usual diet.

Swelling of a particular area due to a local reaction, a change in volume, or tissue changes is called tumefaction. It occurs when tissue fluid or blood collects around injured or irritated tissue, and may be accompanied by pain or localized warmth.

Edema and tumefaction overlap, but their focus differs. Edema refers to an increase in fluid between tissues, while tumefaction refers to a particular area appearing swollen or enlarged as a result. Swelling around the outer ankle bone after an ankle sprain is a typical example of tumefaction.

Most everyday swelling subsides with rest and movement. The following signs differ from ordinary evening swelling, so it is worth having them checked by a professional.

• Sudden swelling in only one leg, with pain or warmth
• Swelling accompanied by shortness of breath or chest tightness
• Sudden swelling of the face and around the eyes, with a change in urine output
• Swelling that does not subside despite rest for several days or longer and gradually increases
• A deep indentation that remains for a long time after pressing