The immune system is essential for good health. It helps prevent infection and disease by finding, destroying and flushing away viruses, bacteria and other germs.
Sometimes the immune system starts attacking healthy cells, tissues and organs. Doctors don't know why it happens, but they do know what it causes—autoimmune diseases.
There are many types of autoimmune diseases, and they can affect almost any part of the body. Some affect only one system or organ, while others affect many parts of the body at once.
Who gets them?
More than 23 million Americans have autoimmune diseases, according to the Office on Women's Health. Women develop them more often than men.
Specific autoimmune diseases may run in families. In other cases a family may be generally prone to having autoimmune diseases, though different family members have different forms.
In addition to genes, many scientists believe triggers such as sun exposure, infections, drugs or pregnancy can be involved.
What types are there?
Examples of autoimmune diseases include:
How are they diagnosed?
No single test can detect an autoimmune disease, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). Diagnosis is usually based on a combination of symptoms, family history, a physical exam and medical tests.
These diseases can be difficult to diagnose at first because the early symptoms—such as fatigue, muscle aches and low fever—can have many other causes.
Can they be treated?
The treatment depends on the specific disease and its severity. The goals of treatment are to relieve symptoms, control the autoimmune process, and maintain the body's ability to fight disease.
Treatment may include:
Researchers continue to explore the causes, prevention and treatment of autoimmune diseases.