What Causes Swelling?

Medically reviewed by George Krucik, MD, MBA

Swelling occurs whenever the organs, skin, or other parts of your body enlarge. It is typically the result of inflammation or a buildup of fluid. Swelling can occur internally, or it can affect your outer skin and muscles. A range of conditions... Read More

What is swelling?

Swelling occurs whenever the organs, skin, or other parts of your body enlarge. It is typically the result of inflammation or a buildup of fluid. Swelling can occur internally, or it can affect your outer skin and muscles.

A range of conditions can cause swelling. Insect bites, illnesses, or injuries often result in external swelling. Internal swelling is often a side effect of medication or the result of a serious injury.

You should seek immediate medical attention if you experience rapid, unexplainable swelling, especially if you also experience unexplained weight gain and pain.

Symptoms of swelling

Sometimes, instances of slight swelling may go unnoticed. This condition does not always cause other symptoms.

For external swelling, the enlargement of skin or muscles is usually visible. However, other signs of swelling include the buildup of fluid in the affected area. An imaging scan can show an enlarged organ, muscle, or bone. A scan can help diagnose internal swelling, which is harder to identify.

If your swelling was caused by an injury, sting, or disease, you might experience a wide range of symptoms. These may include:

  • itching
  • vomiting
  • flatulence
  • pain in the affected area

If the swelling is not visible or if it is internal, you may experience the following symptoms:

  • nausea
  • vomiting
  • dizziness
  • fever
  • fatigue
  • insomnia
  • flu-like symptoms
  • pain

What causes swelling?

Inflammation in your bones, tissues, or muscles can result in external swelling. Cysts and tumors may also cause visible swelling. Although fluid retention is an internal condition, it may also cause external swelling.

The most common causes for external swelling include:

  • insect bites
  • rash
  • hives
  • injury
  • fluid retention
  • pregnancy
  • menstruation
  • hormonal changes
  • infection

External swelling can be localized or widespread.

Localized swelling refers to situations where just one specific area is swollen. For example, a person with an eye infection may experience swelling only around the eyes. A person who has been stung by an insect may experience swelling only in the area of the sting.

Widespread swelling occurs over a large area of the body. This is usually a sign of serious illness. It is often due to fluid retention or an allergic reaction. Other common causes of widespread swelling include:

  • kidney failure
  • heart failure
  • anaphylaxis (severe allergic reaction)
  • venomous insect bite

People with diabetes or certain forms of cancer can experience widespread swelling, or swelling in their extremities, such as their fingers and toes. This form of swelling may appear periodically.

Inside of your body, swelling is often the result of organ inflammation, fluid retention, or flatulence. This can occur in people with chronic diseases such as irritable bowel syndrome, Crohn’s disease, and cancer.

How is swelling diagnosed?

Your doctor may do a variety of tests to diagnose your swelling and its cause. First, they will go over the symptoms you are experiencing and perform a physical examination to check for tenderness in the affected area.

An imaging test, such as an ultrasound, can offer more information about the cause of the swelling. Or more specialized tests, such as a CT scan or MRI, may also provide information on the cause of the swelling.

Imaging tests might reveal blockages in your arteries and veins, inflamed muscle or tissue, or bone fractures. They can also show if you are retaining fluid or have an impacted colon. And your blood and urine will be tested to determine if a disease is causing the swelling.

If a severe allergic reaction is causing your swelling, you will be given an injection of adrenaline before any tests are administered. This medication will stop the reaction from getting any worse.

How is swelling treated?

Your treatment will depend on the cause of the swelling. If a tumor or abscess is causing the swelling, you may need surgery to remove it. If the growth can’t be surgically removed because of its size or location, your doctor may order an aggressive treatment, such as chemotherapy or radiation, to shrink it.

Your doctor might also prescribe medication to relieve inflammation or swelling. Over-the-counter antihistamines can relieve itching and swelling caused by rashes or hives. Topical steroid medication may also be useful in easing skin inflammation. Consult with your doctor if these medications don’t help. You doctor may be able to prescribe a stronger antihistamine.

How is swelling prevented?

If a chronic illness is causing external or internal swelling, you may be able to prevent further swelling by properly managing your illness or by taking medications to treat it. Medication is also used when you have internal swelling as a result of inflammation.

Your doctor may also suggest lifestyle changes to prevent internal swelling. Some at-home measures you can take include avoiding salt, wearing support hose, or keeping your arms and legs above chest level when lying down. 

Medically reviewed by Deborah Weatherspoon, Ph.D, MSN, RN, CRNA on June 28, 2016Written by April Kahn

33 possible conditions

  1. Allergies

    This condition is considered a medical emergency. Urgent care may be required.

    Learn about what causes allergies, the different types of allergies, and how they're treated.


This feature is for informational purposes only and should not be used to diagnose. Please consult a healthcare professional if you have health concerns.

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