The Two Main Causes of Arthritis
Arthritis has two primary causes, and they work in completely different ways. Osteoarthritis happens when the cartilage that cushions your joints wears down over time — usually from years of use, injury, or extra weight on the joint. Rheumatoid arthritis is an autoimmune condition, meaning your immune system mistakenly attacks the lining of your joints, causing inflammation and damage.
Most people over 65 have some osteoarthritis, even if they don't feel symptoms yet. Rheumatoid arthritis is less common but tends to develop earlier in life and affects both sides of your body equally — if your left knee hurts, your right knee usually does too.
There are other forms of arthritis as well, including gout (caused by uric acid crystals in the joint) and lupus-related arthritis, but osteoarthritis and rheumatoid arthritis account for the vast majority of cases.
Key Takeaways
- Osteoarthritis develops when joint cartilage wears down from use, injury, or weight, and is the most common type in older adults.
- Rheumatoid arthritis is an autoimmune disease where your immune system attacks joint linings, causing inflammation on both sides of your body.
- Risk factors for osteoarthritis include age, previous joint injuries, excess weight, and repetitive stress on joints.
- Rheumatoid arthritis risk is linked to genetics, female sex, smoking, and sometimes hormonal changes.
- Knowing which type you have matters because treatment approaches are very different.
How Osteoarthritis Develops Over Time
Osteoarthritis is wear-and-tear arthritis. Your joints are built to move, but the cartilage protecting the bone ends gradually thins. Once cartilage is gone, bone rubs on bone, causing pain, stiffness, and sometimes swelling. This process usually takes years or decades.
The joints most commonly affected are your knees, hips, hands, and spine — the places that bear weight or move repeatedly. A knee injury from a fall or sports accident can speed up osteoarthritis in that joint, even if the injury happened decades earlier. Extra weight puts more pressure on weight-bearing joints, which is why osteoarthritis of the knee is more common in people who carry extra pounds.
Repetitive work also matters. People who spent years doing the same hand motions — assembly line work, typing, or carpentry — often develop osteoarthritis in their hands and wrists earlier than others. Age is the strongest risk factor: cartilage straightforward wears down as you live longer.
Why Rheumatoid Arthritis Attacks Your Joints
Rheumatoid arthritis is fundamentally different because it is not about wear and tear — it is about your immune system. For reasons not fully understood, your body's immune cells begin attacking the synovial membrane, the thin lining inside your joints. This triggers inflammation, swelling, and eventually damage to cartilage and bone.
Rheumatoid arthritis often starts suddenly, sometimes over just a few weeks. You might wake up with swollen, stiff hands or feet that feel worse in the morning. Unlike osteoarthritis, which usually affects one side of your body more than the other, rheumatoid arthritis typically hits both sides equally — both wrists, both knees, both feet.
The condition can also cause fatigue, low-grade fever, and swelling in other parts of your body. If left untreated, rheumatoid arthritis can permanently damage joints, which is why early treatment with disease-modifying drugs makes a real difference in slowing progression.
Genetic and Environmental Risk Factors
Rheumatoid arthritis runs in families. If a parent or sibling has it, your risk is higher — though having the gene does not may provide you will develop the disease. Certain genetic markers, particularly one called HLA-DR4, are more common in people with rheumatoid arthritis.
Smoking is one of the strongest environmental triggers for rheumatoid arthritis, especially in people who carry the genetic risk. Quitting smoking can lower your risk and may slow the disease if you already have it. Hormonal changes also play a role: rheumatoid arthritis is two to three times more common in women than men, and some women notice their symptoms improve during pregnancy (when hormone levels shift) and worsen after delivery.
For osteoarthritis, the main risk factors are age, previous injuries, excess weight, and jobs or sports that stress the same joints repeatedly. Unlike rheumatoid arthritis, osteoarthritis does not run strongly in families, though some people may inherit a tendency toward it.
Other Forms of Arthritis and Their Causes
Gout develops when uric acid builds up in your blood and forms crystals in your joints, usually the big toe. It is triggered by diet (red meat, organ meats, certain seafood, and alcohol raise uric acid), dehydration, and sometimes genetics. Gout attacks come suddenly and are extremely painful, but they are often preventable with medication and dietary changes.
Lupus-related arthritis occurs when systemic lupus erythematosus (an autoimmune disease) affects the joints. It causes pain and swelling but usually does not permanently damage joints the way rheumatoid arthritis does. Psoriatic arthritis develops in some people who have psoriasis (a skin condition) and causes joint pain, swelling, and stiffness.
There are also less common forms like ankylosing spondylitis (which mainly affects the spine) and reactive arthritis (which follows an infection). If you have symptoms that don't fit the typical osteoarthritis or rheumatoid arthritis pattern, your doctor can run blood tests and imaging to narrow down the cause.
How Doctors Determine What Type You Have
Your doctor will ask about when symptoms started, which joints hurt, whether pain is worse in the morning, and whether you have swelling. They will examine your joints and may order blood tests. Rheumatoid arthritis shows up on blood tests as elevated inflammatory markers (like CRP or ESR) and often as positive rheumatoid factor or anti-CCP antibodies. Osteoarthritis typically does not show these markers.
X-rays or ultrasound can show cartilage loss (osteoarthritis) or joint damage from inflammation (rheumatoid arthritis). The pattern of which joints are affected also helps: osteoarthritis often hits one side of your body more, while rheumatoid arthritis is usually symmetrical.
Getting the right diagnosis matters because treatment is very different. Osteoarthritis is managed with pain relief, physical activity, weight management, and sometimes injections. Rheumatoid arthritis requires disease-modifying drugs that slow the immune attack and prevent permanent joint damage.
Frequently Asked Questions
Can you get both osteoarthritis and rheumatoid arthritis at the same time?
Yes, though it is uncommon. Some people develop osteoarthritis from wear and tear and separately develop rheumatoid arthritis from autoimmune causes. Your doctor can tell the difference through blood tests and imaging, and treatment would address both conditions.
Does arthritis always get worse over time?
Osteoarthritis typically progresses slowly, but the rate varies widely — some people have minimal change over years, while others progress faster. Rheumatoid arthritis can worsen quickly if untreated, but modern disease-modifying drugs can slow or even halt progression in many people. Early treatment makes a significant difference.
Can you prevent arthritis if it runs in your family?
You cannot prevent osteoarthritis entirely if genetics play a role, but you can slow it by maintaining a healthy weight, staying active, and protecting joints from injury. For rheumatoid arthritis, quitting smoking and managing stress may lower your risk if you carry genetic factors. There is no may provide prevention, but these steps help.
Is arthritis pain always from inflammation?
In osteoarthritis, pain comes from bone-on-bone friction and sometimes from muscle tightness around the joint, not primarily from inflammation. In rheumatoid arthritis, inflammation is the main driver. This is why anti-inflammatory drugs work better for rheumatoid arthritis than for osteoarthritis, where pain relief and movement are often more effective.