There are more than 100 different types of arthritis. That number surprises most people, who typically think of arthritis as a single condition affecting older adults. In reality, arthritis is an umbrella term for any disease that causes pain, swelling, or stiffness in one or more joints. About 21% of American adults have a diagnosed form of arthritis, and the specific type matters because it determines what’s actually happening inside the joint and how it should be treated.
Two Main Categories: Inflammatory and Non-Inflammatory
The simplest way to sort those 100-plus types is into two broad groups: inflammatory and non-inflammatory. The distinction is practical because the two categories feel different day to day and respond to different treatments.
Inflammatory types, like rheumatoid arthritis and gout, tend to come with fatigue and systemic symptoms beyond just joint pain. Morning stiffness lasts more than an hour and typically improves with movement. Pain is often worst in the morning and eases as you use the joint. Non-inflammatory types, primarily osteoarthritis, follow the opposite pattern. Stiffness is brief (under 30 minutes), pain gets worse with activity throughout the day, and rest brings relief. Non-inflammatory arthritis rarely causes the whole-body fatigue that inflammatory forms do.
Osteoarthritis: The Most Common Type
Osteoarthritis accounts for more visits to doctors’ offices than any other form, generating nearly 10 million primary-diagnosis visits per year in the U.S. alone. It’s sometimes called “wear and tear” arthritis, but the process is more active than that phrase suggests. In a healthy joint, cartilage constantly breaks down and rebuilds in balance. In osteoarthritis, the breakdown side overwhelms the rebuilding side, and the body can’t produce cartilage fast enough to replace what’s lost. Inflammatory signals within the joint accelerate the destruction, so even though osteoarthritis is classified as non-inflammatory, low-grade inflammation plays a role.
The result is cartilage that gradually thins, leaving bone surfaces less cushioned. This is why osteoarthritis develops slowly, worsens with activity, and most commonly affects weight-bearing joints like the knees and hips, along with the hands and spine. Risk rises with age, excess weight, previous joint injuries, and repetitive occupational stress on a joint.
Rheumatoid Arthritis: The Immune System Attacks Joints
Rheumatoid arthritis is the most well-known inflammatory type. The immune system mistakenly targets the synovial membrane, the thin lining that produces fluid to keep joints lubricated. Multiple types of immune cells, including T cells, B cells, and cells that break down bone, get activated and flood the joint lining with inflammatory signals. The lining thickens and swells, eventually damaging cartilage and bone underneath.
Unlike osteoarthritis, rheumatoid arthritis tends to affect joints symmetrically (both wrists, both knees) and often starts in the smaller joints of the hands and feet. It can also affect organs beyond the joints, including the lungs, heart, and eyes. Early, aggressive treatment is important because the joint damage is progressive and harder to reverse once established.
Gout: Crystal Deposits in the Joint
Gout is a form of inflammatory arthritis caused by uric acid crystals that accumulate in a joint. It develops when blood uric acid levels rise above 7.0 mg/dL, the threshold at which uric acid begins crystallizing. Those microscopic crystals trigger intense, sudden inflammation, most commonly in the big toe, knee, or ankle.
A gout flare can go from nothing to excruciating within hours, which is a hallmark that distinguishes it from most other types. Between flares, many people feel completely normal. Over time, though, repeated flares can cause lasting joint damage, and visible deposits called tophi can form under the skin. Keeping uric acid below 6.0 mg/dL generally prevents new crystal deposits. For people who already have visible tophi, the target drops below 5.0 mg/dL.
Psoriatic Arthritis: Skin and Joint Disease Together
Roughly 18% of people with psoriasis develop psoriatic arthritis, though the rate varies widely by region, reaching as high as 27% in North America. It’s more common in adults than children (about 24% versus 9%) and slightly more common in women. In most cases, the skin symptoms appear first, sometimes years before joint pain begins.
Psoriatic arthritis can look very different from person to person. Some people have a few swollen fingers or toes (sometimes called “sausage digits”), while others develop widespread joint inflammation that resembles rheumatoid arthritis. It can also affect the spine and the spots where tendons attach to bone. The underlying immune process involves the same inflammatory pathways that drive psoriasis on the skin, which is why treatments that calm those pathways can improve both the skin and the joints.
Ankylosing Spondylitis: Spine-Centered Arthritis
Ankylosing spondylitis primarily affects the spine and the joints connecting the spine to the pelvis. Over time, chronic inflammation can cause vertebrae to fuse together, reducing flexibility and creating a hunched posture in severe cases. It typically starts in the late teens or twenties, making it one of the few types of arthritis that commonly begins in young adults.
Genetics play an unusually large role. About 85% of people with ankylosing spondylitis carry a specific genetic marker called HLA-B27. Having the gene doesn’t guarantee you’ll develop the condition, but it substantially increases risk. It belongs to a broader family of conditions called spondyloarthritis, which includes several related types that affect the spine, entheses (where tendons meet bone), and sometimes the eyes or digestive tract.
Septic Arthritis: Joint Infection
Septic arthritis is one of the few types that qualifies as a medical emergency. Bacteria, most commonly Staphylococcus aureus, enter a joint through the bloodstream or a wound and trigger rapid, destructive inflammation. In older adults, certain gram-negative bacteria account for 23% to 30% of cases. In younger adults, sexually transmitted bacteria are also a consideration.
The timeline is unforgiving: without appropriate treatment within 24 to 48 hours of symptom onset, the infection can destroy cartilage and the bone underneath, leading to permanent joint damage. Symptoms come on suddenly with a hot, swollen, intensely painful joint, often with fever. Unlike the gradual onset of most other arthritis types, this rapid escalation is a warning sign.
Juvenile Idiopathic Arthritis: Arthritis in Children
Arthritis isn’t limited to adults. Juvenile idiopathic arthritis is the umbrella term for arthritis that begins before age 16 with no identifiable cause. It’s further divided into several subtypes based on how many joints are involved and what other symptoms are present. These include oligoarthritis (four or fewer joints), polyarthritis (five or more joints, with either positive or negative rheumatoid factor), systemic arthritis (joint inflammation plus fevers and rash), enthesitis-related arthritis (inflammation where tendons attach to bone), and psoriatic arthritis.
Some children outgrow the condition, while others carry it into adulthood. The specific subtype strongly influences the outlook and treatment approach.
Other Notable Types
Beyond these major categories, the remaining types of arthritis fill out the count past 100. Reactive arthritis develops after an infection elsewhere in the body, usually in the gut or urinary tract, triggering joint inflammation weeks later. Lupus-related arthritis occurs as part of systemic lupus erythematosus, an autoimmune disease that can affect nearly every organ. Fibromyalgia, while technically not joint inflammation, is sometimes grouped under the arthritis umbrella because it causes widespread musculoskeletal pain and is often managed by rheumatologists.
Other types include arthritis caused by viral infections (like hepatitis or parvovirus), arthritis linked to inflammatory bowel disease, and pseudogout, which resembles gout but involves calcium crystals rather than uric acid. Each of these has distinct triggers, affected populations, and treatment strategies, which is why getting the specific diagnosis right matters more than simply knowing you “have arthritis.”