The Two Main Causes of Arthritis

Arthritis has two primary causes, and which one you have changes how it develops and what happens next. Osteoarthritis happens when the cartilage that cushions your joints wears down over time — usually from decades of use, injury, or excess weight. Rheumatoid arthritis is different: your immune system attacks the lining of your joints by mistake, causing inflammation and damage. These are not the same disease, they do not have the same triggers, and they do not respond to the same treatments.

About 80 percent of people with arthritis have osteoarthritis. It develops slowly, often without you noticing, and tends to affect the knees, hips, hands, and spine — the joints that bear weight or get used most. Rheumatoid arthritis is less common but more aggressive. It can start suddenly, often in middle age, and affects both sides of your body equally (both hands, both knees). It is an autoimmune condition, meaning your body's defense system is misfiring.

Key Takeaways

  • Osteoarthritis is caused by cartilage wearing down from use, injury, or weight, and accounts for the majority of arthritis cases.
  • Rheumatoid arthritis is an autoimmune disease where your immune system attacks joint linings, and it progresses differently than osteoarthritis.
  • Risk factors for osteoarthritis include age, previous joint injury, obesity, and repetitive stress on joints.
  • Rheumatoid arthritis risk is linked to genetics, female sex, smoking, and possibly infections, though the exact trigger is not fully understood.
  • Other less common types of arthritis exist, including gout, lupus-related arthritis, and psoriatic arthritis, each with different causes.

How Osteoarthritis Develops Over Time

Osteoarthritis starts when the smooth cartilage covering the ends of your bones begins to break down. Cartilage is slippery tissue that lets bones glide past each other without friction. When it wears away, bone starts rubbing on bone, which causes pain, stiffness, and swelling. This process usually takes years or decades — you do not wake up with osteoarthritis overnight.

The wear happens because of normal use combined with other factors. A person who runs marathons for 30 years, or works a job that requires standing and repetitive knee bending, puts more stress on cartilage than someone with a desk job. A previous injury — a torn meniscus in the knee, a broken bone that healed unevenly, a dislocated shoulder — can speed up cartilage breakdown in that joint even years later. Excess weight adds pressure to weight-bearing joints like the knees, hips, and lower back, accelerating wear.

Age is a factor, but not the only one. Most people over 65 have some osteoarthritis visible on X-rays, but many feel no pain. A 45-year-old with a knee injury from sports may have more cartilage damage than a sedentary 70-year-old. Genetics matter too — if your parents had osteoarthritis, your risk is higher, possibly because you inherited joint structure or the way your body repairs cartilage.

Why Rheumatoid Arthritis Happens

Rheumatoid arthritis occurs when your immune system mistakenly treats the synovium — the thin lining inside your joints — as a threat and attacks it. This triggers inflammation, swelling, and pain. Over time, the inflammation can damage the cartilage and bone underneath, leading to permanent joint deformity if untreated. Unlike osteoarthritis, which is purely mechanical wear, rheumatoid arthritis is a systemic disease, meaning it can affect your whole body, including your heart, lungs, and eyes.

The exact trigger is not fully known. Genetics play a role — people with a gene called HLA-DR4 or HLA-DRB1 are at higher risk — but having the gene does not may provide you will develop the disease. Something else has to happen to turn it on. Researchers suspect infections (like certain viruses or bacteria), smoking, or hormonal changes may be involved. Women are two to three times more likely to develop rheumatoid arthritis than men, and it often starts during childbearing years or after menopause, suggesting hormones are part of the picture.

Once rheumatoid arthritis starts, it tends to progress steadily if not treated. Early treatment with disease-modifying drugs can slow or even stop the damage, which is why getting a diagnosis quickly matters. Osteoarthritis, by contrast, has no cure but can be managed with exercise, weight management, and pain relief.

Other Types of Arthritis and Their Causes

Beyond osteoarthritis and rheumatoid arthritis, several other conditions cause joint pain and inflammation. Gout happens when uric acid crystals build up in joints, usually the big toe, causing sudden severe pain and swelling. It is triggered by diet (red meat, organ meats, alcohol, sugary drinks), genetics, and kidney function. Psoriatic arthritis develops in some people with psoriasis (a skin condition) when inflammation spreads to the joints. Lupus-related arthritis occurs in people with systemic lupus erythematosus, an autoimmune disease.

Ankylosing spondylitis is a type of inflammatory arthritis that primarily affects the spine, causing stiffness and fusion of vertebrae over time. It is linked to a gene called HLA-B27 and is more common in men. Infectious arthritis (septic arthritis) happens when bacteria, viruses, or fungi enter a joint, usually through an injury or bloodstream infection. This is a medical emergency and requires when ready treatment.

Risk Factors That Increase Your Chances

Several factors raise your risk of developing arthritis, though having a risk factor does not mean you will definitely get it. Age is the strongest predictor for osteoarthritis — the older you are, the more likely cartilage has worn down. Sex matters: women are more likely to develop rheumatoid arthritis, while men are more likely to develop gout and ankylosing spondylitis. Family history increases risk for both osteoarthritis and rheumatoid arthritis, suggesting a genetic component.

Previous joint injury is a major risk factor for osteoarthritis in that specific joint. A knee injury from a car accident or sports can lead to arthritis 10 or 20 years later. Obesity increases risk for osteoarthritis in weight-bearing joints and may also increase rheumatoid arthritis risk. Smoking raises the risk of rheumatoid arthritis and may worsen its progression. Occupation matters if your job involves repetitive joint stress — construction workers, farmers, and assembly line workers have higher osteoarthritis rates in their hands and knees.

What Happens Inside Your Body

In osteoarthritis, the breakdown is mechanical. Cartilage cells (chondrocytes) cannot repair damage as fast as it occurs. The cartilage becomes thin and rough, and small bone spurs (osteophytes) may form at the joint edges. Fluid builds up in the joint, causing swelling. The joint capsule (the tissue surrounding the joint) may tighten, limiting movement. This is why osteoarthritis often gets worse with activity and improves with rest, at least in the early stages.

In rheumatoid arthritis, the process is inflammatory. Your immune system produces antibodies and inflammatory chemicals that attack the synovium. White blood cells flood the joint, causing redness, warmth, and swelling. The inflamed synovium releases enzymes that eat away at cartilage and bone. This is why rheumatoid arthritis often feels worse in the morning (joints are stiff after inactivity) and improves somewhat with movement as the day goes on. The inflammation can also cause fatigue, fever, and loss of appetite.

Frequently Asked Questions

Can arthritis be prevented?

Osteoarthritis risk can be reduced by maintaining a healthy weight, staying active, protecting joints from injury, and avoiding repetitive stress. Rheumatoid arthritis cannot be prevented because the trigger is not fully understood, though not smoking and managing stress may help. If you have a family history, regular check-ups can catch early signs.

Is arthritis hereditary?

Both osteoarthritis and rheumatoid arthritis run in families, but genetics is not destiny. You may inherit a predisposition but never develop the disease, or develop it much later in life. Environmental factors — injury, weight, activity level, smoking — also play a major role.

Can you get arthritis from cracking your knuckles?

No. Cracking knuckles does not cause arthritis. Studies have found no link between the two. The sound comes from gas bubbles in the fluid around your joints, not from damage.

What is the difference between arthritis and arthralgia?

Arthralgia is joint pain without inflammation or structural damage. Arthritis is inflammation of the joint, usually with visible damage on imaging. You can have arthralgia from many causes — overuse, viral infection, fibromyalgia — without having arthritis.

Does cold weather make arthritis worse?

Many people report increased pain in cold weather, though the exact reason is unclear. Possible explanations include lower barometric pressure, reduced activity in cold, muscle stiffness, or thickening of joint fluid. The effect varies by person and is not the same as the cold causing arthritis.