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Swelling: What Your Body is Telling You

Why swelling occurs — and what to do about it

Swollen KneeMost people experience swelling at some time in their lives. Sometimes it's obvious, such as when your ankle balloons after a sprain. And sometimes it's impossible to see, like when airways swell during an asthma attack.

Swelling is your immune system's way of protecting your tissues from harm. Injured tissue releases chemicals that trigger blood vessels to dilate and leak fluid into the damaged area, causing the tissue to swell and preventing damage to surrounding tissue.

But sometimes this response can cause serious problems:

Swollen joints

Take a hard fall and suddenly your wrist or knee is twice its normal size. Luckily, the swelling in most acute injuries goes away as the injury heals. But some diseases, such as rheumatoid arthritis and osteoarthritis, cause chronic joint swelling.

"At the basic level, the immune system's response is the same with each of these diseases, but the causes are different," says Clarence Parks, MD, a pediatrician and general internist at Rush University Medical Center.

Rheumatoid arthritis is an autoimmune disease that can affect the entire body; in people with rheumatoid arthritis, the immune systems attack the lining of the joints and cause swelling.

A class of drugs called disease-modifying antirheumatic drugs is used to treat rheumatoid arthritis by slowing or stopping the immune system’s attack on the joints. This reduces the pain and swelling associated with the disease.

In osteoarthritis, the cartilage between the joints has worn away so that the bones rub together. This irritation causes swelling. "In both conditions the joints are stiff and swollen — but may not be visibly swollen," Parks says. "In chronic inflammation, there is continued or repetitive injury to the affected area. It can be controlled, but it’s not reversible."

Treatment to control the inflammation may include nonsteroidal anti-inflammatory drugs or steroids.

In addition, physicians at Rush have pioneered advanced options such as restoring damaged cartilage to relieve joint pain, and researchers regularly investigate novel treatment options for both osteoarthritis and rheumatoid arthritis. 

Inflamed airways

People with asthma can’t see the inflammation that interferes with their breathing, but they are well aware of how it affects their lives.

Asthma causes chronic inflammation in the airways, the bronchial tubes that carry air into and out of the lungs. This inflammation makes the airways extremely sensitive to substances such as cigarette smoke, mold, dust and air pollution.

During an asthma attack, the airways react to such irritants by becoming even more swollen. The muscles around the bronchial tubes tighten, and cells inside the airways make more mucus. This chain reaction causes the airways to narrow, making breathing difficult.

Fast-acting inhalers, which deliver medication directly to the lungs, can help restore normal breathing by opening the airway and relaxing surrounding muscles, increasing air flow.

"If you need to use your inhaler three times in 10 to 15 minutes, or if your attack is so bad you have to lie down, get medical help right away," Parks says. Researchers don't know what causes asthma, but they think multiple factors play a role, including the following:

  • Having parents who have asthma
  • Having an inherited risk for allergies, called atopy
  • Having contact with certain airborne allergens, such as dust mites, in early childhood
  • Being exposed to certain respiratory or viral infections early in life while the immune system is still developing.

While you may not be able to control all the risk factors for asthma, you may be able to take precautions that delay or even prevent your child from developing it, such as not smoking. Maternal smoking during pregnancy is linked to wheezing in infancy, and children who are exposed to secondhand smoke in the home are also more likely to develop asthma.

Brain injury

Your immune system reacts to brain trauma the same way it reacts to any injury — with inflammation. "But because the brain is encased in the skull, the swollen tissue can't expand, and swelling in the brain has nowhere to go," Parks says.

The swelling causes increased pressure in the brain, called intracranial pressure, which can be life-threatening. Breathing, heart rate and blood pressure can be affected as the swelling restricts blood flow to the brain and puts pressure on regions that maintain life-sustaining functions.

Physicians at Rush use a treatment called cooling therapy to bring down swelling. With this treatment, cooling blankets or other methods are used to lower the internal body temperature about nine degrees. This helps prevent further damage to the brain by reducing intracranial pressure. 

"Cooling the body slows the metabolic activity, decreases blood flow to the injury and reduces swelling," Parks says.

Learn more about traumatic brain injury.

Allergic reactions

An allergen is anything that triggers an allergic response. Allergies usually start in childhood, but you can develop an allergy at any age to just about any substance. In some cases, allergies may go into remission only to reappear later in life, or they can get worse over time.

Here's how allergic response happens:

  • Antibodies — blood proteins that circulate in the bloodstream and exist in most body fluids — are part of the immune system and help capture foreign intruders. If you have allergies, you have an antibody for each allergen to which you are sensitive.
  • The antibody, called immunoglobulin E (IgE), attaches to cells that release chemicals, including histamine, which produce the symptoms of an allergic reaction. There the IgE wait for their allergen.
  • The next time the allergic person comes in contact with the allergen, the IgE captures it, triggering the cells to release their chemicals, causing symptoms such as sneezing, coughing and swelling.
  • The reaction often doesn’t stop there. The chemicals mobilize other inflammatory cells to the site, which, in turn, produce more inflammation.

In rare cases, an allergy can cause a life-threatening complication called anaphylactic shock. This is a whole-body response to an allergen, such as an insect sting. Symptoms develop quickly and include a drop in blood pressure and swelling of the throat and tongue — cutting off the airway.

"If you know you or your child has a severe allergy, you should always carry an EpiPen and avoid the allergen at all costs," Parks says.

Available by prescription, an EpiPen has medication in it called epinephrine that can open your airways. Even after using epinephrine, it's important to seek emergency medical help because one dose may not be enough.

Related: An allergy specialist at Rush debunks some common myths about allergies.