Arthritis is inflammation or degeneration of one or more joints. The word itself comes from Greek: “arthro” meaning joint, and “itis” meaning inflammation. But in practice, arthritis isn’t a single disease. It’s an umbrella term covering more than 100 conditions that cause pain, swelling, and stiffness in the joints. About 21% of American adults have been diagnosed with some form of it.
What Happens Inside an Arthritic Joint
A healthy joint is lined with a thin membrane called the synovium, normally just two to three cell layers thick, with almost no inflammatory cells present. In arthritis, this lining thickens dramatically as immune cells flood in. Blood vessels in the area become more permeable, allowing fluid and proteins to leak into the joint space. The result is swelling, warmth, and pain.
What makes arthritis progressive is a self-reinforcing cycle. Damage to cartilage releases tiny fragments into the joint fluid. Those fragments trigger more inflammation, which causes more cartilage breakdown, which releases more fragments. Cartilage breakdown products appear in the joint long before any damage shows up on imaging, meaning the process can be well underway before you feel significant symptoms.
The Most Common Types
Osteoarthritis is the most common form. It involves the gradual wearing away of cartilage, the smooth tissue that caps the ends of bones where they meet. Without that cushion, bones eventually grind against each other. Osteoarthritis typically develops in weight-bearing joints like the knees and hips, and in the hands. It’s often described as “wear and tear” arthritis, though inflammation plays a larger role than that phrase suggests.
Rheumatoid arthritis works differently. It’s an autoimmune condition where the immune system mistakenly attacks the lining of the joints. Rather than cartilage breaking down from mechanical stress, the body’s own defenses cause the damage. Rheumatoid arthritis tends to affect joints symmetrically (both wrists, both knees) and can also cause fatigue and affect organs beyond the joints.
Gout is another common form, caused by uric acid crystals that accumulate in a joint, most often the big toe. These needle-shaped crystals trigger an intense immune response. White blood cells swarm the crystals, releasing inflammatory signals that cause rapid, severe swelling and pain. Gout attacks often come on suddenly, sometimes overnight.
Symptoms Across All Types
Despite having different causes, most forms of arthritis share a core set of symptoms: joint pain, stiffness, swelling, reduced range of motion, and sometimes skin discoloration around the affected joint. The pattern of these symptoms helps distinguish one type from another.
Morning stiffness is a useful clue. In osteoarthritis, stiffness after rest usually eases within about 30 minutes. In rheumatoid arthritis, morning stiffness commonly lasts an hour or more. Pain that worsens with activity points toward osteoarthritis, while pain and stiffness that improve with movement lean more toward inflammatory types like rheumatoid arthritis.
Arthritis Isn’t Only an Older Person’s Disease
While osteoarthritis becomes more common with age, arthritis can develop at any stage of life. Juvenile arthritis is defined as arthritis of unknown cause beginning before a child’s 16th birthday and persisting for at least six weeks. Some forms involve not just joint inflammation but also fever, rash, and enlarged lymph nodes. Rheumatoid arthritis most commonly appears between ages 30 and 60, and gout can strike adults of any age.
Risk Factors That Increase Your Chances
Several factors raise the likelihood of developing arthritis. Carrying extra weight puts more mechanical stress on the knees and hips, making osteoarthritis in those joints significantly more common. A previous joint injury, even one that healed well, increases the risk of osteoarthritis in that same joint later. ACL tears in the knee are a well-documented example.
Genetics matter too, especially for autoimmune forms. Having a family history of rheumatoid arthritis, lupus, or ankylosing spondylitis (a type of arthritis in the spine) raises your risk. You can’t change your genes or undo a past injury, but maintaining a healthy weight is one modifiable factor that clearly reduces risk and slows progression in osteoarthritis.
How Arthritis Is Diagnosed
Diagnosis usually starts with a physical exam and a detailed history of your symptoms, including which joints hurt, when the pain started, and whether stiffness is worse in the morning. From there, blood tests and imaging help narrow down the type.
For suspected rheumatoid arthritis, blood tests check for markers of inflammation, such as C-reactive protein (CRP) and a measure called sed rate that reflects how much inflammation is happening systemwide. Other blood tests look for specific antibodies, including rheumatoid factor and anti-CCP antibodies, which are strongly associated with rheumatoid arthritis. X-rays can track joint damage over time, while MRI and ultrasound reveal soft tissue changes and inflammation that X-rays miss. Osteoarthritis, by contrast, is usually diagnosed based on symptoms and X-ray findings without needing blood work.
How Arthritis Is Managed
Treatment depends entirely on the type. For osteoarthritis, the first line is usually physical therapy, weight management, and over-the-counter pain relievers like ibuprofen. These medications reduce pain and stiffness but don’t slow the underlying cartilage loss. In advanced cases, joint replacement surgery becomes an option.
Rheumatoid arthritis requires a different strategy. Because the immune system is driving the damage, treatment focuses on disease-modifying drugs that suppress or redirect immune activity. These medications don’t just relieve symptoms. They slow or stop the joint destruction itself. The tradeoff is that they take several weeks to months to reach full effect, so faster-acting anti-inflammatory drugs are often used as a bridge in the early weeks. Newer biologic therapies target specific parts of the immune response and have expanded options considerably for people who don’t respond to older medications.
For gout, treatment centers on lowering uric acid levels to prevent crystals from forming, alongside anti-inflammatory drugs to manage acute flare-ups. Dietary changes, particularly reducing alcohol and foods high in purines like red meat and shellfish, can help keep uric acid in check.
Across all types, regular physical activity consistently improves joint function and reduces pain. Low-impact exercise like swimming, cycling, and walking strengthens the muscles around joints without adding excessive stress. Staying active is one of the most effective things you can do regardless of which type of arthritis you have.