There are more than 100 conditions that fall under the umbrella of arthritis, but five types account for the vast majority of cases: osteoarthritis, rheumatoid arthritis, psoriatic arthritis, gout, and ankylosing spondylitis. Roughly 67 million adults in the United States, about 28% of the population aged 20 and older, have been diagnosed with some form of arthritis. Each type has a different cause, affects the body differently, and calls for a different approach to treatment.
Osteoarthritis
Osteoarthritis is the most common type by a wide margin. It develops when the protective cartilage that cushions the ends of your bones breaks down over time. In a healthy joint, the body constantly builds new cartilage and removes old cartilage in a balanced cycle. In osteoarthritis, that balance tips toward destruction. Enzymes that break down cartilage become overactive, overwhelming the body’s ability to repair the damage. This creates a self-reinforcing loop: the more cartilage degrades, the more inflammatory signals are released, which accelerates further breakdown.
The joints that bear the most weight or see the most repetitive use are hit hardest: knees, hips, the lower back, and the small joints of the hands. Symptoms usually develop gradually. You might notice stiffness after sitting for a while, pain that worsens with activity, or a grating sensation when you move the joint. Unlike inflammatory types of arthritis, osteoarthritis pain tends to feel worse at the end of the day rather than first thing in the morning.
Risk factors include age, previous joint injuries, obesity, and family history. There’s no way to regrow lost cartilage, so treatment focuses on slowing the damage and managing pain through exercise, weight management, physical therapy, and in some cases joint replacement surgery when the cartilage is severely worn.
Rheumatoid Arthritis
Rheumatoid arthritis is an autoimmune disease. Instead of protecting you from infection, the immune system turns on your own joint tissue. Immune cells flood the joint lining, releasing inflammatory chemicals called cytokines that cause swelling, pain, and a general feeling of fatigue and being unwell. Over time, this chronic inflammation can erode bone and deform the joint permanently if left untreated.
The hallmark of rheumatoid arthritis is symmetrical joint involvement. If your left wrist is swollen, your right wrist will likely follow. It most commonly targets the small joints of the hands, wrists, and feet, though it can affect larger joints too. Morning stiffness is a key distinguishing feature. While osteoarthritis stiffness fades within a few minutes of moving, rheumatoid arthritis stiffness often lasts 30 minutes or longer.
Diagnosis involves blood tests alongside a physical exam. One test looks for a marker called anti-CCP, which is 97% specific for rheumatoid arthritis when positive. Another test checks for rheumatoid factor, though about 20% of people with confirmed rheumatoid arthritis will have a normal result on that test, and 5% of people without the disease will test positive. Imaging and symptom patterns fill in the gaps.
Treatment typically starts with disease-modifying medications that suppress the overactive immune response. These come in two broad categories: conventional options that have decades of safety data behind them, and newer biologic medications designed to block specific parts of the immune system driving the inflammation. Both can be effective on their own or in combination, and the choice often depends on symptom severity, cost, and how you respond to initial treatment. The goal is to catch the disease early enough to prevent joint damage.
Psoriatic Arthritis
Psoriatic arthritis develops in people who have psoriasis, the skin condition that causes red, scaly patches. Skin symptoms come first in roughly 80% of cases, sometimes years before joint pain appears. That makes dermatologists often the first clinicians to spot early warning signs.
One of the most recognizable symptoms is dactylitis, sometimes called “sausage digits,” where an entire finger or toe swells so dramatically it looks like a sausage. Dactylitis is considered a hallmark of the condition and helps distinguish it from rheumatoid arthritis. Nail changes are another clue: pitting, thickening, separation of the nail from the nail bed, and ridges are all more common in people with psoriatic arthritis than in those with psoriasis alone.
Psoriatic arthritis doesn’t always follow the symmetrical pattern of rheumatoid arthritis. It can affect joints on just one side of the body, the spine, or the spots where tendons and ligaments attach to bone. The range of symptoms is wide, from mild and manageable to severe and disabling. Treatment overlaps with rheumatoid arthritis in many ways, relying on immune-modifying medications, but the approach is tailored to address both skin and joint symptoms together.
Gout
Gout is caused by a buildup of uric acid in the blood. When levels get too high, uric acid forms needle-shaped crystals that deposit in and around joints. The result is sudden, intense pain that often strikes without warning, frequently in the big toe. A gout flare can wake you up in the middle of the night with a joint so swollen and tender that even the weight of a bedsheet feels unbearable.
Flares typically peak within 12 to 24 hours and can last days to weeks. Between attacks, you may feel completely fine. But if uric acid levels stay elevated over time, flares become more frequent, affect more joints, and can lead to permanent joint damage and visible deposits of uric acid crystite under the skin called tophi.
Diet plays a meaningful role. Foods high in purines, like red meat, organ meats, shellfish, and alcohol (especially beer), increase uric acid production. Staying hydrated, limiting those triggers, and maintaining a healthy weight all help keep levels in check. For people with frequent flares or very high uric acid, medications can lower uric acid production or help the kidneys clear it more efficiently. Gout is one of the most treatable forms of arthritis when managed consistently.
Ankylosing Spondylitis
Ankylosing spondylitis primarily targets the spine and the joints where the spine connects to the pelvis (the sacroiliac joints). It causes inflammation that, over time, can lead to new bone formation. In severe cases, sections of the spine can fuse together, reducing flexibility and locking the back into a hunched-forward position.
Symptoms usually begin in the late teens or twenties, making it unusual among arthritis types. The pain is worst at night and in the early morning, improving with movement and exercise rather than rest. This pattern is a key diagnostic clue. Stiffness in the lower back that improves as you get moving is characteristic.
Genetics play a strong role. More than 8 in 10 people with ankylosing spondylitis carry a gene variant called HLA-B27. About 8% of the general population carries this variant, but most never develop the condition. If you have ankylosing spondylitis and carry the gene, there’s roughly a 50% chance you’ll pass the variant to your children, though only 5 to 10% of children who inherit it will go on to develop the disease.
Regular exercise, particularly stretching and posture work, is one of the most effective ways to maintain spinal mobility. Physical therapy focused on range of motion can make a significant difference. For persistent inflammation, the same classes of immune-modifying and biologic medications used for rheumatoid and psoriatic arthritis are also effective here, targeting the inflammatory pathways that drive bone fusion.
How These Types Overlap and Differ
The five types split into two broad categories. Osteoarthritis is a mechanical, wear-and-tear condition driven by cartilage breakdown. The other four, rheumatoid arthritis, psoriatic arthritis, gout, and ankylosing spondylitis, are all driven by inflammation, though the triggers differ. Rheumatoid and psoriatic arthritis involve an immune system that attacks healthy tissue. Gout is a crystal-deposit disease. Ankylosing spondylitis is an inflammatory condition with a strong genetic component.
These distinctions matter because they determine treatment. Anti-inflammatory and immune-suppressing medications that work well for rheumatoid arthritis won’t address the uric acid problem behind gout. Physical therapy that’s essential for ankylosing spondylitis plays a different role in osteoarthritis. Getting an accurate diagnosis is the first step toward the right treatment plan, and many people live with one type for years before it’s correctly identified. If you have persistent joint pain, stiffness, or swelling, especially if it follows one of the patterns described above, that information can help guide the conversation with your doctor toward faster answers.