Arthritis is a condition that causes pain and stiffness of the joints. Sometimes it also causes redness, swelling, and warmth. In severe cases, joints may become misshapen.

There are different kinds of arthritis. Two common forms are osteoarthritis and rheumatoid arthritis (RA). Both of these forms of arthritis are more common in women than in men.

Examples of other forms of arthritis include gout, ankylosing spondylitis, and arthritis that happens after an injury or with some infections such as gonorrhea.

Osteoarthritis is a disease in which the cartilage in joints breaks down. Cartilage is the joint's cushion. It covers the ends of bones and allows free movement. If cartilage becomes rough, frays, or wears away, bones grind against each other. As a result, the joint becomes irritated and swollen (inflamed). Sometimes the irritation causes abnormal bone growths, called spurs. Bone spurs increase swelling. Osteoarthritis normally affects the feet, knees, lower back, hips, and fingers. Symptoms of the disease start to appear by middle age. Most people over age 60 have some osteoarthritis, but they may not have symptoms.

Rheumatoid arthritis (RA) affects the lining of the joints. It is an autoimmune disease. This means that the body's defenses against infection attack the body's own tissue. Rheumatoid arthritis causes redness and swelling, stiffness, and misshapen joints. It usually affects the joints of the hands, arms, and feet. RA usually starts in early adulthood or middle age.