There are more than 100 different types of arthritis. That number surprises most people, who tend to think of arthritis as a single disease. In reality, “arthritis” is an umbrella term covering a wide range of conditions that cause joint pain, swelling, or stiffness. These types fall into several broad categories based on what’s actually causing the joint damage.
The Major Categories of Arthritis
While the 100-plus types can seem overwhelming, most fall into a handful of groups: degenerative (wear-and-tear), autoimmune and inflammatory, crystal-based (metabolic), infectious, and those linked to other diseases. Understanding which category a type belongs to matters because the underlying cause, and therefore the treatment approach, differs dramatically between them.
About 21.3% of U.S. adults have been diagnosed with some form of arthritis, which works out to roughly 53 million people. Here’s what the most common categories look like.
Degenerative Arthritis: Osteoarthritis
Osteoarthritis is by far the most common type, affecting 32.5 million adults in the U.S. alone. It happens when the cartilage cushioning the ends of your bones gradually wears down over time. Without that smooth buffer, bones begin grinding against each other, causing pain, stiffness, and reduced range of motion.
Osteoarthritis most often develops in the knees, hips, hands, and spine. Age is the biggest risk factor, but joint injuries, obesity, and repetitive stress on a joint can accelerate the process. Unlike inflammatory types, osteoarthritis tends to feel worse after activity and better with rest. Morning stiffness, when it occurs, typically fades within about 30 minutes, which is one of the ways doctors distinguish it from inflammatory forms.
Autoimmune and Inflammatory Types
In autoimmune arthritis, the immune system attacks the lining of the joints by mistake, causing inflammation that can eventually erode bone and cartilage. Rheumatoid arthritis (RA) is the most well-known type in this group. It typically affects joints symmetrically, meaning if one wrist is inflamed, the other usually is too. A hallmark feature is morning stiffness lasting longer than one hour, which signals an inflammatory process rather than simple wear and tear.
Blood tests can help identify RA. One key marker, called anti-CCP, is found in about 67% of people with RA and is highly specific to the disease (95% specificity). Another marker, rheumatoid factor, can appear in the blood years before symptoms start. One study found that nearly 30% of people who later developed RA had detectable rheumatoid factor a median of 4.5 years before diagnosis.
Other autoimmune types include psoriatic arthritis, which develops in some people with the skin condition psoriasis, and lupus-related arthritis. Lupus can cause joint pain and swelling that looks similar to RA, but it’s generally intermittent and usually doesn’t cause permanent joint damage.
Spondyloarthritis: Spine-Centered Types
Spondyloarthritis is a family of inflammatory types that primarily target the spine and the points where tendons and ligaments attach to bone. Ankylosing spondylitis is the most recognized form, causing chronic back pain and stiffness that typically starts in the lower back and sacroiliac joints. Over time, it can cause vertebrae to fuse together, limiting mobility.
A gene variant called HLA-B27 significantly raises the risk of developing ankylosing spondylitis, though carrying the gene doesn’t guarantee the disease. About 75% of children who inherit HLA-B27 from an affected parent never develop the condition. Psoriatic arthritis and a type called enthesitis-related arthritis (common in children) also fall under this umbrella.
Crystal Arthritis: Gout and Pseudogout
Crystal arthritis develops when microscopic crystals form inside a joint, triggering intense inflammation. The two main types are gout and pseudogout, and they’re caused by different crystals entirely.
Gout results from a buildup of uric acid in the blood. When levels get too high, uric acid forms sharp crystals that deposit in joints, most famously the big toe. Attacks come on suddenly, often overnight, with severe pain, redness, and swelling. Pseudogout, on the other hand, is caused by calcium pyrophosphate crystals rather than uric acid. It tends to affect larger joints like the knee and wrist. Over time, pseudogout can damage cartilage, leading to chronic joint pain as bone rubs against bone. Despite similar symptoms during a flare, the two conditions require different management because the underlying chemistry is different.
Infectious Arthritis
Infectious (septic) arthritis happens when bacteria, viruses, or fungi enter a joint directly, usually through the bloodstream, a wound, or during surgery. It causes rapid-onset pain, swelling, and warmth in a single joint, often the knee. This type is a medical emergency because the infection can destroy joint cartilage quickly if untreated.
Reactive arthritis is a related but distinct condition. Rather than an infection inside the joint itself, it’s an inflammatory reaction triggered by an infection somewhere else in the body. Common bacterial triggers include chlamydia (from a urogenital infection) and several gut bacteria like salmonella, shigella, campylobacter, and E. coli. Joint symptoms typically develop one to four weeks after the initial infection and can be accompanied by eye inflammation and urinary symptoms.
Juvenile Arthritis
Arthritis isn’t limited to adults. Juvenile idiopathic arthritis (JIA) is the term for arthritis that begins before age 16 with no identifiable cause. It’s classified into seven subtypes: systemic-onset JIA, persistent or extended oligoarthritis (affecting four or fewer joints), two forms of polyarthritis (distinguished by whether rheumatoid factor is present), psoriatic JIA, enthesitis-related arthritis, and an undifferentiated category for cases that don’t fit neatly into the others.
Systemic-onset JIA stands apart because it affects the whole body, causing fevers and rashes alongside joint inflammation. Enthesitis-related arthritis in children targets the spots where tendons meet bone and carries a risk of eye inflammation (iritis) that requires monitoring. Many children with JIA improve significantly as they grow, though some carry the condition into adulthood.
Arthritis Linked to Other Conditions
Many of the 100-plus types are actually joint symptoms of broader diseases. Lupus, inflammatory bowel disease, and Sjögren’s syndrome can all cause arthritis as one feature of a larger systemic illness. These types are sometimes called secondary arthritis because the joint inflammation is a consequence of the primary condition rather than the main problem. Treatment focuses on managing the underlying disease, which often improves joint symptoms as well.
Fibromyalgia is frequently grouped alongside arthritis in patient resources, though it doesn’t cause joint inflammation or damage. It produces widespread pain and tenderness that can mimic arthritis, which is why the two are often confused. The distinction matters because the treatment strategies are fundamentally different.