What is swelling?

Swelling is an increase in the size or a change in the shape of an area of the body. Swelling can be caused by:

• A collection of body fluid.
• Growth of tissue.
• Abnormal movement or position of tissue.

Most people will have swelling at some time. When it's hot and you've stood or sat in the same position for a long time, you might notice swelling in your feet and ankles. Staying in one position for any length of time increases the risk that the lower legs, feet, or hands will swell. That's because gravity normally causes body fluid to move down a limb. Swelling can also be caused by heat-related problems. One example is heat edema from working or being active in a hot environment.

Body fluid can collect in different tissue spaces of the body (localized swelling). Or it can affect the whole body (generalized swelling). Causes of localized swelling include:

• Injury to a specific body area. Bruising (hematoma) from an injury is caused by tears in the small blood vessels under the skin. Bleeding can also affect the joint (hemarthrosis) or the area that cushions and lubricates the joint (traumatic bursitis). Swelling can affect just one area. Or it may involve large sections of the body, such as swelling that occurs after a car crash.
• Infection. It can occur in a joint or under the skin. An abscess is a pocket of pus that forms at the site of infected tissue. Cellulitis is a skin infection that can cause mild or severe swelling.
• Burns. They can cause swelling at the site of the burn or in a larger area around the burn.
• Inflammation that occurs when tissue is irritated by overuse or repeated motion.
  • Swelling of the tendon and swelling caused by a series of small tears around a tendon (tendinosis) can occur together or on their own.
  • Swelling of the sac that cushions and lubricates the joint (bursitis) can be caused by prolonged or repeated pressure. It can also be caused by activities that require repeated twisting or rapid joint movements.
• Insect bites or stings. Most insect bites or stings cause a small amount of redness or swelling. Some people have an allergic reaction to a bite or sting. They have a lot of swelling, redness, and itching.
• Other causes, such as swelling related to a sac-shaped structure with clear fluid, blood, or pus (cyst). Or swelling may be from a swollen gland, such as a salivary gland.

Causes of generalized swelling include:

• An allergic reaction. Sudden swelling of the hands and face may be a severe allergic reaction (anaphylaxis). It needs medical care right away.
• Autoimmune diseases, such as lupus, rheumatoid arthritis, and scleroderma. These diseases can cause swelling when the body produces antibodies and other cells that attack and destroy tissues in the body.
• Medicines. Some medicines change how body fluids circulate, causing swelling. Swelling may also occur as an allergic reaction to a medicine.
• Circulation problems related to certain medical conditions, such as peripheral arterial disease, heart failure, diabetes, or kidney disease. Thrombophlebitis causes swelling of an extremity when a blood clot interrupts blood flow in a vein in the arm or leg.
• Fluid that accumulates in the belly (ascites) because of other problems, such as malnutrition, cirrhosis, or liver disease.

Some people may have swelling as a reaction to a medical treatment, procedure, or surgery. Swelling from a medical treatment may be related to the procedure. Or it may be from a substance, such as dye, used during the procedure. Swelling may occur at an intravenous (I.V.) site used during a procedure or at an I.V. site used for medicines given at home. Some swelling at the site of surgery is normal, such as swelling of the arm after a mastectomy. Lymphedema is swelling that occurs in an area around lymph nodes that have been removed (such as after surgery) or injured (such as after radiation treatments).

Swelling can also be caused by the rise and fall of hormone levels within the body. Some women may notice swelling from retaining fluid during their menstrual cycles. This may be called cyclical edema, because it's related to the menstrual cycle. Some women have mild swelling in their hands or feet during pregnancy. Swelling in the feet may be more obvious in the third trimester of the pregnancy. Generalized swelling can be a sign of a pregnancy-related problem called preeclampsia.

Swelling can occur when tissues move out of their normal position, such as hernias in the abdomen.

Most of the time, swelling is mild and goes away on its own. You may not even know what caused it. Home treatment is usually all that is needed to relieve mild symptoms.