There are more than 100 conditions that fall under the umbrella of “arthritis,” but most cases fit into a handful of major types. An estimated 58.5 million U.S. adults have some form of arthritis, and the type you have determines everything from how it feels to how it’s treated. Here’s a breakdown of the most common kinds and what sets each one apart.
Osteoarthritis
Osteoarthritis is by far the most common type. It develops when the cartilage cushioning your joints gradually breaks down. Enzymes in the joint tissue slowly degrade the two main structural proteins in cartilage: collagen (which gives it strength) and proteoglycan (which helps it absorb shock). Once collagen is damaged, it can’t repair itself, making this an irreversible step in the disease.
As cartilage wears away, tiny fragments float into the joint fluid, triggering low-grade inflammation in the surrounding tissue. The bone underneath the cartilage also changes over time, thickening and forming bony spurs at the edges of the joint. This process isn’t just a consequence of cartilage loss. There’s growing evidence that abnormal bone cell behavior plays an active role in driving the disease forward.
Osteoarthritis most commonly affects the knees, hips, hands, and spine. It tends to develop gradually after age 50, though prior joint injuries can trigger it much earlier. The hallmark symptoms are stiffness after rest, pain that worsens with activity, and a grating or crunching sensation in the joint. Unlike inflammatory types of arthritis, osteoarthritis rarely causes significant swelling or warmth.
Rheumatoid Arthritis
Rheumatoid arthritis (RA) is an autoimmune disease. Your immune system mistakenly attacks the lining of your joints, causing persistent inflammation that can eventually erode bone and deform the joint. It typically strikes symmetrically, meaning if one wrist is affected, the other usually is too. The small joints of the hands and feet are often hit first.
Two blood markers help identify RA. Rheumatoid factor (RF) is found in roughly 69% of people with the disease, with a specificity of about 85%, meaning it’s a useful clue but not definitive on its own. The other marker, anti-CCP antibodies, tends to be more specific. A strongly positive RF (more than three times the upper limit of normal) is more telling than a weakly positive one. Some people have RA with completely negative blood tests, a form called seronegative RA, which can be harder to diagnose.
RA often comes with fatigue, low-grade fever, and general malaise alongside joint symptoms. Without treatment, the joint damage it causes is progressive and can become severe within a few years. Early, aggressive treatment with immune-modulating medications has dramatically improved long-term outcomes.
Gout
Gout is caused by the buildup of uric acid crystals inside a joint. Your body produces uric acid when it breaks down certain foods and its own cells. Normally, uric acid dissolves in the blood and leaves through the kidneys. But when blood levels rise above about 6.8 mg/dL, the saturation point, uric acid can crystallize and deposit in soft tissues and joints.
A gout attack is hard to miss. The joint, most classically the base of the big toe, becomes intensely painful, red, swollen, and hot, often peaking within 12 to 24 hours. Between attacks, you can feel completely fine for weeks or months. Over time, untreated gout can lead to permanent joint damage and chalky deposits of uric acid crystite called tophi under the skin. Diet, genetics, kidney function, and certain medications all influence your risk.
Pseudogout
Pseudogout mimics gout but involves a different crystal entirely: calcium pyrophosphate. These crystals tend to deposit in larger joints like the knee, wrist, or shoulder rather than the big toe. The attacks look similar, with sudden pain, swelling, and warmth, but the underlying cause and treatment differ. Unlike gout, there’s no medication that targets the root cause of crystal buildup in pseudogout, unless it’s linked to an underlying condition like iron overload or overactive parathyroid glands. Treatment focuses on managing inflammation during flares.
Psoriatic Arthritis
Psoriatic arthritis (PsA) develops in some people with psoriasis, the skin condition that causes red, scaly patches. It can appear before, after, or at the same time as skin symptoms. PsA has two distinctive features that separate it from other types of inflammatory arthritis.
The first is dactylitis, sometimes called “sausage fingers” or “sausage toes,” where an entire finger or toe swells uniformly rather than just at the joint. The second is enthesitis, inflammation where tendons and ligaments attach to bone. Common spots include the Achilles tendon, the bottom of the heel, and the elbows. Enthesitis is considered an early manifestation of PsA and is linked to worse outcomes and reduced quality of life. PsA can also affect the spine and the joints closest to the fingernails, and it sometimes causes pitting or separation of the nails themselves.
Ankylosing Spondylitis
Ankylosing spondylitis (AS) primarily targets the spine and the joints where the spine meets the pelvis (the sacroiliac joints). It causes chronic back pain and stiffness that typically starts in the late teens or twenties, is worse in the morning, and improves with movement rather than rest. Over time, inflammation can cause new bone to form between vertebrae, gradually fusing sections of the spine together and limiting flexibility.
Genetics play a strong role. About 85% of people with AS carry the HLA-B27 gene, compared to roughly 8% of the general European population. Having the gene doesn’t mean you’ll develop the disease, but it significantly increases susceptibility. AS can also cause inflammation in the eyes, heart, and lungs, though joint and spine symptoms dominate the picture.
Lupus-Related Arthritis
Systemic lupus erythematosus (lupus) frequently causes joint pain and swelling, particularly in the hands, wrists, and knees. In fact, joint involvement is one of the most common reasons people with lupus first seek medical attention. The key difference from rheumatoid arthritis is that lupus-related arthritis typically does not cause bone erosion or permanent joint deformities. The inflammation tends to be migratory, moving from joint to joint, and it responds to treatment aimed at controlling the broader autoimmune disease.
Juvenile Idiopathic Arthritis
Arthritis doesn’t only affect adults. Juvenile idiopathic arthritis (JIA) is diagnosed in children under 16 and encompasses several distinct subtypes. Oligoarthritis affects four or fewer joints and is the most common form in young children. Polyarthritis involves five or more joints and can be either RF-positive or RF-negative. Systemic arthritis causes joint inflammation along with high spiking fevers and rash. Other subtypes include enthesitis-related arthritis (similar to ankylosing spondylitis in adults), psoriatic arthritis, and undifferentiated arthritis for cases that don’t fit neatly into another category.
Each subtype behaves differently, and outcomes range widely. Some children outgrow their symptoms entirely, while others carry the disease into adulthood. Early treatment is important for preventing joint damage during critical growth years.
How Doctors Tell Them Apart
The starting point is usually your pattern of symptoms: which joints are involved, whether the pain is symmetrical, how quickly it came on, and whether you have other symptoms like skin changes, fever, or back stiffness. Blood tests look for inflammation markers and specific antibodies. Imaging with X-rays, ultrasound, or MRI can reveal erosion, crystal deposits, or new bone formation.
When the diagnosis is unclear, joint fluid analysis can be decisive. A sample of fluid is drawn from the swollen joint and examined under a microscope. Fluid with fewer than 2,000 white blood cells per microliter points toward a non-inflammatory cause like osteoarthritis. Higher counts suggest inflammatory or infectious arthritis. The presence of needle-shaped uric acid crystals confirms gout, while rhombus-shaped calcium pyrophosphate crystals confirm pseudogout.
Getting the type right matters because treatments are fundamentally different. Anti-inflammatory drugs may help with symptoms across the board, but osteoarthritis management centers on physical therapy and joint preservation, while autoimmune forms like RA and PsA require medications that calm the immune system. Gout is one of the few types that can be effectively “cured” by keeping uric acid levels low enough to prevent crystal formation entirely.