There are more than 100 types of arthritis, but most fall into a handful of major categories based on what’s actually happening inside the joint. An estimated 67 million U.S. adults have been diagnosed with some form of arthritis, and osteoarthritis alone accounts for nearly half of all cases. Understanding which type you’re dealing with matters because the causes, progression, and treatment differ significantly from one form to another.
Osteoarthritis
Osteoarthritis is the most common type, affecting roughly 33 million American adults. It’s often called “wear and tear” arthritis, but the reality is more complex than simple friction. In a healthy joint, the body constantly breaks down and rebuilds cartilage in a balanced cycle. In osteoarthritis, the enzymes responsible for breaking down cartilage become overactive and overwhelm the body’s ability to repair itself. The result is a net loss of the proteins that give cartilage its structure and cushioning ability.
The damage starts at the surface of the cartilage, where tiny cracks and rough patches appear. Over time, these progress into deeper layers, eventually creating large areas of eroded cartilage that expose the underlying bone. The joints most commonly affected are knees, hips, hands, and the spine. Inflammatory signals within the joint speed up the process, triggering cartilage cells to self-destruct and producing compounds that further accelerate deterioration.
Risk factors include age, excess body weight, prior joint injuries, and repetitive stress from certain occupations or sports. Symptoms develop gradually: stiffness after sitting, pain that worsens with activity, and eventually reduced range of motion. Unlike some other forms of arthritis, osteoarthritis tends to affect individual joints rather than causing widespread inflammation throughout the body.
Rheumatoid Arthritis
Rheumatoid arthritis is the second most common form, affecting about 10.6 million U.S. adults. It’s an autoimmune disease, meaning the immune system mistakenly attacks the lining of your own joints. This lining, called the synovium, becomes inflamed and thickened, gradually damaging cartilage and bone from the inside out.
The pattern is distinctive. Rheumatoid arthritis typically strikes the same joints on both sides of the body, often starting in the small joints of the fingers and toes before moving to wrists, elbows, knees, and ankles. Morning stiffness lasting longer than 30 minutes is a hallmark. Because it’s a systemic disease, you may also experience fatigue, low-grade fever, and inflammation in other organs like the eyes or lungs. Without treatment, joint damage can become permanent within the first two years, which is why early diagnosis and aggressive management are important.
Gout
Gout is a form of inflammatory arthritis caused by a buildup of uric acid in the blood. When levels exceed roughly 6.8 mg/dL, uric acid can crystallize and deposit in joints. These needle-shaped crystals trigger intense, sudden attacks of pain, redness, and swelling, most famously in the big toe, though ankles, knees, and wrists are also common targets.
A gout flare often starts in the middle of the night. The affected joint becomes so tender that even the weight of a bedsheet can feel excruciating. Attacks typically peak within 12 to 24 hours and may resolve on their own within a week or two, but without management, flares tend to become more frequent and affect more joints over time. Chronic gout can eventually lead to visible lumps of urate crystals under the skin and permanent joint damage. Dietary factors like red meat, shellfish, and alcohol (especially beer) raise uric acid levels, though genetics play a significant role in how efficiently your kidneys clear uric acid.
Psoriatic Arthritis
Psoriatic arthritis develops in some people who have the skin condition psoriasis, characterized by red, scaly patches. In most cases, the skin symptoms appear first, sometimes years before joint problems begin. The arthritis itself can range from mild to severe and affects joints in an asymmetric pattern, meaning it might involve a knee on one side and a wrist on the other.
Two features set psoriatic arthritis apart from other types. The first is dactylitis, where an entire finger or toe swells up like a sausage rather than just the joint itself. The second is enthesitis, inflammation at the points where tendons and ligaments attach to bone. The Achilles tendon and the bottom of the foot are common spots. Nail changes like pitting, crumbling, or separation from the nail bed are another strong clue. Psoriatic arthritis can cause permanent joint damage if left untreated, but it responds well to medications that target the underlying immune dysfunction.
Ankylosing Spondylitis
Ankylosing spondylitis primarily targets the spine, starting with the sacroiliac joints where the pelvis meets the base of the spine. Inflammation in these joints, called sacroiliitis, causes deep, aching low back pain and stiffness that’s worst in the morning or after long periods of inactivity. Unlike a pulled muscle, this pain improves with movement and exercise rather than rest.
Over time, the inflammation can cause new bone to form along the spine, gradually fusing vertebrae together and limiting flexibility. In severe cases, the spine can become rigid in a forward-curved position. Ankylosing spondylitis has a strong genetic component: a gene variant called HLA-B27 significantly increases risk, though most people who carry this gene never develop the condition, and some people with ankylosing spondylitis don’t carry it at all. Symptoms typically begin in the late teens or twenties, making it unusual among arthritis types for striking younger adults. Regular exercise and physical therapy are critical for maintaining spinal mobility.
Juvenile Idiopathic Arthritis
Juvenile idiopathic arthritis is the umbrella term for arthritis that begins before age 16 and lasts at least six weeks with no other identifiable cause. It’s not a single disease but a group of subtypes, each with a different pattern. The major forms include systemic arthritis (which causes high fevers and rash along with joint inflammation), oligoarthritis (affecting four or fewer joints), polyarthritis (five or more joints), psoriatic arthritis, enthesitis-related arthritis, and undifferentiated arthritis.
Oligoarthritis is the most common subtype and often affects large joints like the knee. Systemic arthritis is less common but more serious, causing body-wide inflammation that can affect the heart, liver, and lymph nodes. Many children with juvenile idiopathic arthritis eventually go into remission, but some carry active disease into adulthood. Eye inflammation is a frequent complication that requires regular screening, since it can develop without obvious symptoms.
Reactive Arthritis
Reactive arthritis develops as a reaction to an infection elsewhere in the body, typically in the digestive tract, urinary tract, or genitals. The bacteria most commonly linked to it are Salmonella, Campylobacter, Shigella, Yersinia, and Chlamydia, though only a small fraction of people infected with these organisms ever develop joint symptoms.
Joint pain and swelling typically appear one to six weeks after the initial infection, which has usually cleared by the time the arthritis shows up. This delay can make the connection easy to miss. Reactive arthritis often affects the knees, ankles, and feet, and may come with eye redness and urinary discomfort. Most cases resolve within a few months to a year, though some people experience recurring flares or develop chronic symptoms.
Lupus-Related Arthritis
Systemic lupus erythematosus, commonly called lupus, is an autoimmune disease that can affect nearly every organ. Joint pain and swelling are among the most common symptoms, occurring in the vast majority of people with the condition. Lupus arthritis feels similar to rheumatoid arthritis and tends to affect the same small joints of the hands and wrists.
One important distinction: lupus arthritis is traditionally considered non-erosive, meaning it causes pain and swelling but generally doesn’t destroy bone and cartilage the way rheumatoid arthritis does. The joints may become very painful and stiff during flares but typically don’t sustain permanent structural damage. That said, lupus brings its own set of serious concerns, including kidney inflammation, blood clotting problems, and skin sensitivity to sunlight, so the arthritis is just one piece of a larger picture.
Septic Arthritis
Septic arthritis is a joint infection, usually caused by bacteria that enter through the bloodstream, a wound, or surgery. It’s a medical emergency. Unlike other forms of arthritis that develop over weeks or months, septic arthritis comes on rapidly with severe pain, swelling, warmth, and fever, typically in a single joint. The knee is the most frequently affected.
Diagnosis requires analyzing fluid drawn from the joint. In bacterial joint infections, the white blood cell count in that fluid is typically above 50,000 cells per cubic millimeter, far higher than in most other forms of inflammatory arthritis. Prompt treatment with antibiotics is essential to prevent permanent cartilage destruction, which can happen within days. People with existing joint disease, artificial joints, or weakened immune systems face the highest risk.
How the Types Compare
- Cause: Osteoarthritis stems from cartilage breakdown. Rheumatoid arthritis, psoriatic arthritis, lupus, and ankylosing spondylitis are autoimmune. Gout is metabolic. Septic and reactive arthritis are infection-related.
- Age of onset: Osteoarthritis and gout become more common after 40 to 50. Ankylosing spondylitis and reactive arthritis often appear in the twenties. Juvenile idiopathic arthritis starts before 16.
- Joint pattern: Rheumatoid arthritis is symmetric (both sides). Psoriatic arthritis is often asymmetric. Osteoarthritis targets weight-bearing joints and hands. Ankylosing spondylitis focuses on the spine.
- Speed of onset: Gout and septic arthritis come on suddenly, over hours. Osteoarthritis and ankylosing spondylitis develop gradually over months or years.