Arthritis affects the movements you rely on for everyday activities. Arthritis is usually chronic. This means that it can last on and off for a lifetime. There are over 100 kinds of arthritis that can affect many different areas of the body. In addition to the joints, some forms of arthritis are associated with diseases of other tissues and organs in the body. People of all ages, including children and young adults, can develop arthritis.

Inflammation is a reaction of the body that causes swelling, redness, pain, and loss of motion in an affected area. It is the major physical problem in the most serious forms of arthritis. Normally, inflammation is the way the body responds to an injury or to the presence of disease agents, such as viruses or bacteria. During this reaction, many cells of the body's defense system rush to the injured area to wipe out the cause of the problem, clean up damaged cells and repair tissues that have been hurt. Once the "battle" is won, the inflammation normally goes away and the area becomes healthy again.

In many forms of arthritis, the inflammation does not go away as it should. Instead, it becomes part of the problem, damaging healthy tissues of the body. This may result in more inflammation and more damage - a continuing cycle. The damage that occurs can change the bones and other tissues of the joints, sometimes affecting their shape and making movement hard and painful. Diseases in which the immune system malfunctions and attacks healthy parts of the body are called autoimmune diseases.