Arthritis has two main causes, and they work differently

Osteoarthritis happens when the cartilage that cushions your joints wears down over time. Rheumatoid arthritis happens when your immune system attacks the lining of your joints. These are not the same disease, they do not have the same cause, and they do not respond to the same treatment. Most people have one or the other, though a small number have both.

The reason this matters is that understanding which type you have changes what your doctor will recommend and what you can realistically expect from treatment. A worn joint and an inflamed joint need different approaches.

Key Takeaways

  • Osteoarthritis develops when joint cartilage breaks down from repeated use, age, injury, or excess weight, and it is the most common type.
  • Rheumatoid arthritis is an autoimmune disease where your body's immune system mistakenly attacks joint linings, causing inflammation and damage.
  • Other types of arthritis—including gout, lupus-related arthritis, and psoriatic arthritis—have different causes ranging from uric acid buildup to genetic factors.
  • Risk factors like age, family history, previous injuries, and lifestyle habits influence whether you develop arthritis, but they do not may provide it.

How osteoarthritis develops: wear and tear on joints

Osteoarthritis is mechanical wear. Your joints have cartilage—a smooth, slippery tissue that lets bones move without friction. Over decades, that cartilage thins and cracks. Once it is damaged, the bone underneath can rub directly against bone, which causes pain, stiffness, and swelling.

This happens fastest in joints that carry your weight or move repeatedly: knees, hips, lower back, and hands. A person who spent 30 years on their feet at work will often develop knee osteoarthritis earlier than someone in an office. A previous injury—a torn meniscus, a broken bone, a bad sprain—can speed up cartilage breakdown in that specific joint, sometimes years later.

Age is the strongest predictor. Cartilage does not repair itself well, so damage accumulates. Most people over 60 have some osteoarthritis visible on X-rays, though not all of them feel pain. Excess weight adds pressure to weight-bearing joints, which accelerates wear. A person who is 30 pounds overweight puts extra stress on knees and hips with every step.

How rheumatoid arthritis develops: your immune system attacks your joints

Rheumatoid arthritis is autoimmune. Your immune system normally protects you from infection. In rheumatoid arthritis, something goes wrong and your immune system treats the lining of your joints—called the synovium—as a threat. It sends inflammatory cells to attack it.

This causes the synovium to swell, produce excess fluid, and release chemicals that damage cartilage and bone. Unlike osteoarthritis, which is usually one-sided (your left knee or right hip), rheumatoid arthritis typically affects joints on both sides of your body at the same time. Your hands, wrists, feet, and knees are common targets.

The cause of the immune system malfunction is not fully understood. Genetics play a role—if a parent or sibling has rheumatoid arthritis, your risk is higher. Certain genes make the condition more likely, but having the gene does not mean you will develop it. Environmental triggers may also matter: some research suggests infections or smoking can activate the disease in people who are genetically vulnerable.

Other types of arthritis and their causes

Gout develops when uric acid—a waste product from food and your body's normal metabolism—builds up in your blood and forms crystals in joints. These crystals trigger sudden, severe inflammation, usually in the big toe. Diet (especially red meat, organ meats, and alcohol), dehydration, and certain medications increase uric acid levels.

Psoriatic arthritis occurs in people with psoriasis, a skin condition. The same immune system problem that causes the skin rash also attacks joints. Lupus arthritis is part of systemic lupus erythematosus, another autoimmune disease that affects multiple body systems. Ankylosing spondylitis is an inflammatory arthritis that primarily affects the spine and is strongly linked to a specific gene called HLA-B27.

These less common types share a pattern: they involve either immune system dysfunction or metabolic imbalance, not simple wear and tear. They often appear earlier in life than osteoarthritis and may affect multiple joints or organs at once.

Risk factors that increase your chances of developing arthritis

Age is unavoidable—the longer you live, the more likely cartilage wears down. Family history matters for both osteoarthritis and rheumatoid arthritis, though genetics is not destiny. A parent with arthritis raises your risk, but many people with the genetic predisposition never develop symptoms.

Previous joint injuries are a concrete risk factor. A torn ligament, a fracture, or a severe sprain can damage cartilage or change how a joint moves, leading to osteoarthritis in that joint later. Excess weight increases pressure on knees, hips, and ankles. Repetitive motion—from sports, manual labor, or certain jobs—can accelerate wear in specific joints.

For rheumatoid arthritis, smoking is a documented risk factor, especially in people with genetic vulnerability. Some infections may trigger the disease in susceptible people, though the exact mechanism is still being studied. Sex also plays a role: rheumatoid arthritis is more common in women, while gout is more common in men.

Why some people develop arthritis and others do not

Risk factors are not guarantees. Two people with the same family history, age, and weight can have very different outcomes. One develops arthritis and the other does not. This is because arthritis results from a combination of factors—genetics, environment, injury history, lifestyle, and sometimes chance.

For osteoarthritis, the wear happens at different rates in different people. Some cartilage is more resilient. Some people's bodies repair damage better. For rheumatoid arthritis, the immune system trigger remains mysterious in many cases. A person might carry the genetic risk for decades and never develop symptoms, or symptoms might appear after a specific infection or life stress.

This unpredictability is frustrating, but it also means that having risk factors does not mean arthritis is inevitable. Maintaining a healthy weight, staying active, protecting joints from injury, and avoiding smoking are all evidence-based ways to reduce your risk or slow progression if arthritis has already started.

Frequently Asked Questions

Can arthritis be caused by weather or cold?

No. Cold weather does not cause arthritis, though people with existing arthritis often report that their pain feels worse in cold or damp conditions. This may be due to changes in air pressure or how cold affects muscle stiffness, but it is not the cause of the disease itself.

Does arthritis run in families?

Yes, for both osteoarthritis and rheumatoid arthritis. Having a parent or sibling with arthritis increases your risk, but it is not automatic. Genetics loads the gun, but environment and lifestyle pull the trigger.

Can you get arthritis from cracking your knuckles?

No. Cracking your knuckles does not cause arthritis. Studies have found no link between the habit and arthritis development, even in people who crack their knuckles for decades.

Is arthritis always caused by age?

No. While osteoarthritis is more common as you age, rheumatoid arthritis and other autoimmune types can appear in young adults or even children. Age increases risk for wear-and-tear arthritis, but it is not the only cause.

What is the difference between arthritis caused by injury and arthritis from age?

An injury can damage cartilage directly or change how a joint moves, speeding up wear in that specific joint. Age-related arthritis develops slowly across multiple joints from decades of use. An injury can trigger arthritis in one joint while the rest of your body remains unaffected.