Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the bodys tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area may feel heavy, and joint stiffness. Other symptoms depend on the underlying cause.Causes may include venous insufficiency, heart failure, kidney problems, low protein levels, liver problems, deep vein thrombosis, infections, angioedema, certain medications, and lymphedema. It may also occur after prolonged sitting or standing and during menstruation or pregnancy. The condition is more concerning if it starts suddenly, or pain or shortness of breath is present.Treatment depends on the underlying cause. If the underlying mechanism involves sodium retention, decreased salt intake and a diuretic may be used. Elevating the legs and support stockings may be useful for edema of the legs. Older people are more commonly affected. The word is from the Greek οἴδημα oídēma meaning swelling. Signs and symptoms
Specific area
An edema will occur in specific organs as part of inflammations, tendinitis or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms. Examples of edema in specific organs:

Peripheral edema (dependent edema of legs) is extracellular fluid accumulation in the legs. This can occur in otherwise healthy people due to hypervolemia or maintaining a standing or seated posture for an extended period of time. It can occur due to diminished venous return of blood to the heart due to congestive heart failure or pulmonary hypertension.
These include estrogens, thereby including drugs for hormone replacement therapy or the combined oral contraceptive pill, as well as non-steroidal anti-inflammatory drugs and beta-blockers.Premenstrual water retention, causing bloating and breast tenderness, is common. Mechanism
Six factors can contribute to the formation of edema:
increased hydrostatic pressure;
reduced colloidal or oncotic pressure within blood vessels;
increased tissue colloidal or  oncotic pressure;
increased blood vessel wall permeability (such as inflammation);
obstruction of fluid clearance in the lymphatic system;
changes in the water-retaining properties of the tissues themselves. Raised hydrostatic pressure often reflects retention of water and sodium by the kidneys.Generation of interstitial fluid is regulated by the forces of the Starling equation. Hydrostatic pressure within blood vessels tends to cause water to filter out into the tissue. This leads to a difference in protein concentration between blood plasma and tissue. As a result, the colloidal or oncotic pressure of the higher level of protein in the plasma tends to draw water back into the blood vessels from the tissue. Starlings equation states that the rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance. Most water leakage occurs in capillaries or post capillary venules, which have a semi-permeable membrane wall that allows water to pass more freely than protein. (The protein is said to be reflected and the efficiency of reflection is given by a reflection constant of up to 1.)