context: Did you know that there are more than 100 types of arthritis? Learn about some of the most common forms, including what they are, what happens, and their symptoms. What is it? More people have this condition than any other form of arthritis. It's the "wear and tear" that happens when your joints are overused. It usually happens with age, but it can also come from joint injuries or obesity, which puts extra stress on your joints. Joints that bear weight -- like your knees, hips, feet, and spine -- are the most common places it affects. It often comes on gradually over months or years. It makes the affected joint hurt. But you don't feel sick or have the fatigue that comes with some other types of arthritis. What happens: You lose your body's shock absorber. Cartilage, the slippery material that covers the ends of bones, gradually breaks down. One example is what can happen to your knees when you're overweight. The extra pounds put more pressure on the cartilage as it gets squeezed between the bones. It gets damaged and wears away, so there isn't as much left to cushion the joint. The damaged cartilage makes movement painful. You may hear a grating sound when the roughened cartilage on the surface of the bones rubs together. You may get painful spurs or bumps on the end of the bones, especially on fingers and feet. The joint lining can get inflamed, but it's not common with osteoarthritis. Symptoms depend on which joint or joints are affected. You may have: Deep, aching pain Trouble dressing, combing your hair, gripping things, bending over, squatting, or climbing stairs, depending on which joints are involved Morning stiffness that typically lasts less than 30 minutes Pain when walking Stiffness after resting Your joint may be: Warm to the touch Swollen and harder to move Unable to move through a full range of motion What is it? RA is an autoimmune disease. That means the immune system attacks parts of the body, especially the joints. That leads to inflammation, which can cause severe joint damage if you don't treat it. About 1 out of every 5 people who have rheumatoid arthritis get lumps on their skin called rheumatoid nodules. These often form over joint areas that receive pressure, such as over knuckles, elbows, or heels. What happens: Doctors don't know exactly what causes RA. Some experts believe the immune system becomes "confused" after an infection with a bacteria or virus and starts to attack your joints. This battle can spread to other areas of the body. Scientists think two of the body's chemicals that are related to inflammation, tumor necrosis factor ( TNF) and interleukin-1, trigger other parts of the immune system in rheumatoid arthritis. Medicines that block TNF, interleukin-1, and interleukin-6 can improve the symptoms and prevent joint damage. Symptoms can come on gradually or start suddenly. They're often more severe than with osteoarthritis. The most common include: Pain, stiffness, and swelling in your hands, wrists, elbows, shoulders, knees, ankles, feet, jaw, and neck. Rheumatoid arthritis usually affects multiple joints. More than one swollen joint. Usually, it's small joints in your wrists, hands, or feet. A symmetrical pattern. When the knuckles on your left hand are inflamed, the knuckles on your right hand probably will be as well. After some time, you may notice more of your joints feel warm or become painful or swollen. Morning stiffness than can last for hours or even most of the day. You may also feel fatigued and notice that your appetite is down and you've lost weight. What is it? People with this condition have inflammation of the skin (psoriasis) and joints (arthritis). Psoriasis causes patchy, raised, red and white areas of inflamed skin with scales. It usually affects the tips of the elbows and knees, the scalp, the navel, and skin around the genital areas or anus. Only about 10% to 30% of people with psoriasis will also get psoriatic arthritis. What happens: This type of arthritis usually starts between ages 30 and 50, but it can start as early as childhood. It's equally common among men and women. The skin disease (psoriasis) usually shows up first. Symptoms: Psoriatic arthritis can swell the fingers and toes. People who have it often have fingernails that are pitted or discolored, too. In some people, only one joint or a few joints are affected. For example, you could have it in only one knee. Sometimes, it affects the spine or just the fingers and toes. What is it? A buildup of uric acid crystals in a joint. Most of the time, it's your big toe or another part of your foot. What happens: Often you wake up with a sudden, sharp pain in your big toe after a night of drinking. But drugs, stress, or another illness can also trigger a gout attack. The attack will last between 3 and 10 days, even if you don't treat it. It may be months or years before you have another one, but over time, attacks will grow more frequent. And they may last longer, too. If gout goes untreated too long, it can affect your joints and kidneys. Gout results from one of three things: Your body is making more uric acid. Your kidneys can't process the uric acid your body makes. You're eating too many foods that raise uric acid levels. Symptoms: They almost always come on quickly. You'll notice: Intense joint pain: It'll probably be in your big toe, but it could also be in your ankles, knees, elbows, wrists, or fingers. Discomfort: Even after the sharp pain goes away, your joint will still hurt. Inflammation and redness: The joint will be red, swollen, and tender. Hard to move: Your joint will be stiff. What is it? Lupus (also called SLE or systemic lupus erythematosus) is an autoimmune disease. It can affect your joints and many organs in your body. What happens: Doctors don't know exactly what causes lupus, but something makes your immune system go awry. Instead of attacking viruses and other invaders, it starts to cause inflammation and pain throughout your body, from your joints, to your organs, to your brain. Women of childbearing age are more likely to get lupus than men. It affects African- American women more often than white women. It usually appears between ages 15 and 44. Symptoms: Painful, swollen joints Fatigue Headaches Swelling in the feet, legs, hands, or around the eyes Rashes, including a "butterfly" rash across the cheeks Mouth sores Sun sensitivity Hair loss Blue or white fingers or toes when exposed to cold ( Raynaud's phenomenon) Blood disorders, like anemia and low levels of white blood cells or platelets Chest pain from inflammation of the lining of the heart or lungs