There are more than 100 types of arthritis, but most fall into a handful of major categories: degenerative, autoimmune/inflammatory, metabolic, and infectious. About 21% of U.S. adults have been diagnosed with some form of arthritis, making it one of the most common chronic conditions. Understanding which type you’re dealing with matters because the causes, progression, and treatments differ significantly from one type to the next.
Osteoarthritis
Osteoarthritis is the most common type and the one most people picture when they hear the word “arthritis.” It happens when the cartilage and other tissues inside a joint break down and change structure over time. Cartilage is the smooth, slippery tissue that cushions the ends of bones where they meet. As it deteriorates, the underlying bone becomes exposed, making the joint painful to move and gradually reducing range of motion.
Older explanations described this as simple “wear and tear,” but researchers now understand it differently. Changes in the tissue itself trigger the breakdown process, which is why some people develop severe osteoarthritis while others with equally active lifestyles never do. The exact trigger for those tissue changes is still unknown. Osteoarthritis most commonly affects large, weight-bearing joints like the knees and hips, along with the neck, lower back, and hands. Pain typically worsens with activity and improves with rest, which is one way to distinguish it from inflammatory types.
Rheumatoid Arthritis
Rheumatoid arthritis is an autoimmune disease, meaning the immune system mistakenly attacks the body’s own tissues. Specifically, it targets the synovium, a thin membrane lining the joint capsule that produces fluid to keep joints lubricated. The immune system sends antibodies to the synovium, causing inflammation that can eventually damage cartilage and bone.
Unlike osteoarthritis, rheumatoid arthritis can strike at any age and tends to affect joints symmetrically (both wrists, both knees). It also goes beyond the joints. Many people experience fatigue, low-grade fever, and loss of appetite. Over time, the disease can affect the skin, eyes, lungs, heart, and blood vessels. This systemic nature is a key difference from osteoarthritis, which stays localized to the affected joints.
Diagnosis often involves blood tests. Rheumatoid factor is a common screening marker, though some people with confirmed rheumatoid arthritis test negative for it, a situation called seronegative RA. A more specific test, anti-CCP, has about 95% specificity, meaning most positive results are accurate. Treatment centers on disease-modifying drugs that slow or stop the immune system’s attack on the joints, often starting with methotrexate. If that isn’t enough after three to six months, biologic drugs that target specific parts of the immune response are typically added.
Psoriatic Arthritis
Psoriatic arthritis develops in some people who have psoriasis, the skin condition that causes red, scaly patches. It can also appear before any skin symptoms show up, which makes it tricky to identify early. The hallmark feature is dactylitis, sometimes called “sausage fingers” or “sausage toes,” where an entire digit swells up rather than just a single joint. This occurs in roughly 16% to 49% of people with psoriatic arthritis.
Dactylitis tends to show up asymmetrically, affects the feet more than the hands, and often involves multiple digits at once. In some cases, it’s the very first sign of psoriatic arthritis and may be the only symptom for months or even years before other joints become involved. Psoriatic arthritis is associated with more aggressive joint erosion when dactylitis is present, so early recognition matters.
Gout
Gout is a metabolic form of arthritis caused by a buildup of uric acid in the blood. Normally, uric acid dissolves in the bloodstream and passes through the kidneys into urine. When the body produces too much or the kidneys don’t clear enough, uric acid accumulates and forms sharp, needle-like crystals in a joint or the surrounding tissue. These crystals cause sudden, intense pain, swelling, and redness.
The joint at the base of the big toe is the most common target, especially during a first flare. Gout attacks often come on overnight, and the pain can be severe enough to wake you from sleep. Between attacks, you may feel completely normal. Over time, without management, flares can become more frequent and affect additional joints. Reducing uric acid levels through dietary changes and, when needed, medication can prevent crystal formation and stop flares from recurring.
Ankylosing Spondylitis
Ankylosing spondylitis primarily affects the spine and the sacroiliac joints, which connect the base of the spine to the pelvis. Chronic inflammation in these areas can eventually cause vertebrae to fuse together, reducing flexibility and creating a hunched posture in severe cases. Symptoms usually begin in early adulthood with persistent low back pain and stiffness, particularly in the morning or after periods of inactivity. Unlike mechanical back pain, the discomfort from ankylosing spondylitis tends to improve with movement rather than rest.
A genetic marker called HLA-B27 is closely associated with this condition. About 80% to 90% of people with ankylosing spondylitis carry this gene, though having the gene doesn’t guarantee you’ll develop the disease. Diagnosis typically involves imaging of the sacroiliac joints and spine, combined with blood tests and a physical exam.
Lupus-Related Arthritis
Systemic lupus erythematosus, commonly called lupus, is an autoimmune disease that can affect nearly every organ system. Joint pain and arthritis are among the most frequent symptoms. Lupus arthritis is typically symmetric and involves multiple joints, which can make it look similar to rheumatoid arthritis on the surface. The key difference is that lupus arthritis is generally nonerosive, meaning it causes pain and swelling without permanently destroying bone and cartilage the way rheumatoid arthritis can.
Diagnosis relies partly on antinuclear antibody testing. A positive result is one of the criteria for a lupus diagnosis, while a negative result effectively rules lupus out for most people. However, a positive antinuclear antibody test alone doesn’t confirm lupus, since the marker can appear in other autoimmune conditions as well.
Juvenile Idiopathic Arthritis
Arthritis isn’t limited to adults. Juvenile idiopathic arthritis is a group of conditions characterized by joint inflammation that begins before age 16. It includes several subtypes: oligoarticular (affecting four or fewer joints), polyarticular (five or more joints), enthesitis-related (inflammation where tendons and ligaments attach to bone), psoriatic, systemic, and undifferentiated forms. Systemic juvenile idiopathic arthritis stands out because it causes body-wide symptoms like high spiking fevers and rash in addition to joint inflammation.
The word “idiopathic” means the cause is unknown, which is true for most cases. Some children outgrow the condition, while others carry it into adulthood. Early treatment focuses on controlling inflammation to prevent joint damage during critical growth years.
Septic Arthritis
Septic arthritis is a joint infection, most commonly caused by bacteria. Staphylococcus and Streptococcus species are the usual culprits, though viruses and fungi can also be responsible. It typically affects a single joint, causing rapid-onset pain, swelling, warmth, and fever. This type is a medical emergency. Without appropriate treatment within 24 to 48 hours of onset, the infection can destroy cartilage, erode bone, and cause permanent joint damage. Bacteria can reach a joint through the bloodstream from an infection elsewhere in the body, through a wound near the joint, or as a complication of joint surgery.
How These Types Are Told Apart
Distinguishing between types of arthritis involves a combination of symptom patterns, physical examination, imaging, and blood work. The pattern of joint involvement is one of the strongest initial clues. Osteoarthritis favors large weight-bearing joints and the hands. Rheumatoid arthritis typically appears symmetrically in smaller joints first. Gout targets the big toe. Ankylosing spondylitis centers on the spine and pelvis.
Blood tests help narrow the diagnosis further. Rheumatoid factor and anti-CCP point toward rheumatoid arthritis. HLA-B27 is associated with ankylosing spondylitis and related conditions. Antinuclear antibodies suggest lupus. Elevated uric acid levels support a gout diagnosis. None of these markers are perfectly specific on their own, which is why diagnosis usually requires combining lab results with the clinical picture. If you’re experiencing persistent joint pain, swelling, or stiffness, the type of arthritis you have shapes every decision about treatment, so getting the right diagnosis early is worth the effort.