Arthritis develops when the protective cartilage in your joints wears down or when your immune system attacks the joint lining

Arthritis is not a single disease — it is a group of conditions that damage joints in different ways. The two most common types, osteoarthritis and rheumatoid arthritis, have completely different causes, though both end in pain and stiffness. Understanding which type you have, or which type runs in your family, helps explain why the damage happened and what you might do about it.

Osteoarthritis happens when years of use wear down the cartilage that cushions the ends of your bones. Rheumatoid arthritis happens when your immune system mistakenly attacks the lining of your joints. There are also less common types — gout, lupus-related arthritis, and others — each with its own trigger. Knowing the cause matters because it shapes what treatment might help and whether the damage can be slowed.

Key Takeaways

  • Osteoarthritis is caused by wear and tear on cartilage over time, usually in joints you use most, and becomes more common as you age.
  • Rheumatoid arthritis is an autoimmune disease where your body attacks joint linings, and it often runs in families or is triggered by infection or stress.
  • Gout develops when uric acid crystals build up in joints, usually triggered by diet, dehydration, or certain medications.
  • Risk factors like excess weight, previous joint injury, repetitive motion, and family history increase your chances of developing arthritis.
  • Age is the strongest predictor of osteoarthritis, but younger people can develop rheumatoid arthritis or other types at any time.

How osteoarthritis develops from joint wear and tear

Osteoarthritis is the most common type of arthritis. It happens when the cartilage that covers the ends of your bones gradually breaks down. Cartilage is smooth and slippery — it lets bones glide past each other without friction. Over decades of movement, that cartilage thins. Eventually, bone rubs against bone, causing pain, swelling, and stiffness.

This process is not the same as normal aging. Many people live into their 80s and 90s without severe osteoarthritis, while others develop it in their 50s. The speed depends on how much stress you put on a joint, whether you injured it before, your weight, and your genes. Joints that bear your weight — knees, hips, lower back — wear out faster than others. Joints you use repeatedly in work or sports also wear down sooner.

Once cartilage is gone, it does not grow back. That is why early treatment focuses on slowing the damage: keeping the joint moving, managing weight to reduce stress, and sometimes using medication to ease pain and inflammation. Physical activity, even gentle movement, often helps more than complete rest, because movement keeps the joint lubricated and muscles strong enough to support it.

Why rheumatoid arthritis is an immune system attack on joints

Rheumatoid arthritis (RA) is an autoimmune disease. Your immune system normally protects you by attacking germs and invaders. In RA, something goes wrong — your immune system attacks the synovium, the thin lining inside your joints. This lining becomes inflamed, swollen, and painful. Over time, the inflammation can damage the cartilage and bone underneath.

No one knows exactly why the immune system turns against the joints. Researchers believe a combination of genes and environmental triggers is involved. If your parents or siblings have RA, your risk is higher. Infections — particularly respiratory infections — may trigger RA in people who are genetically vulnerable. Stress, smoking, and hormonal changes (especially in women around menopause) may also play a role. RA often starts suddenly, sometimes after a stressful event or illness.

Unlike osteoarthritis, RA can develop at any age, including in children and young adults. It also tends to affect multiple joints at once, often on both sides of the body — both hands, both knees. Early treatment with medications that calm the immune system can slow or even stop the damage, which is why seeing a doctor early matters more with RA than with osteoarthritis.

Gout: when uric acid crystals form in joints

Gout is arthritis caused by a buildup of uric acid in your blood. Uric acid is a waste product your body makes when it breaks down purines, substances found in certain foods and drinks. Normally, your kidneys filter uric acid out through urine. But if your kidneys do not work well, or if you consume too much uric acid, it builds up. The excess uric acid forms needle-shaped crystals that deposit in joints, usually starting in the big toe.

Gout attacks come on suddenly — often at night — with intense pain, redness, and swelling. The attack usually lasts a few days to a week, then goes away on its own. But if uric acid stays high, attacks come back more often and may damage the joint permanently.

Diet plays a big role in gout. Red meat, organ meats, seafood, alcohol (especially beer), and sugary drinks all raise uric acid. Dehydration also increases risk. Certain medications — including diuretics used for high blood pressure and low-dose aspirin — can trigger gout. Men are more likely to develop gout than women, and risk rises with age. If you have a family history of gout, your risk is higher.

Other types of arthritis and their causes

Beyond the three main types, several other forms of arthritis have distinct causes. Lupus is an autoimmune disease that can inflame joints, skin, kidneys, and other organs. Psoriatic arthritis develops in some people who have psoriasis, a skin condition. Ankylosing spondylitis primarily affects the spine and is linked to a specific gene. Infectious arthritis can follow a bacterial or viral infection — Lyme disease, for example, can cause arthritis if untreated.

These less common types account for a smaller share of arthritis cases, but they are important to recognize because treatment differs. If you develop joint pain after an infection, tick bite, or skin rash, mention it to your doctor. Some of these conditions respond well to early treatment but can cause lasting damage if missed.

Risk factors that increase your chances of developing arthritis

Several factors make arthritis more likely, though having a risk factor does not mean you will definitely develop it. Age is the strongest predictor of osteoarthritis — the older you are, the more likely you are to have it. Family history matters for both osteoarthritis and rheumatoid arthritis; if a parent or sibling has arthritis, your risk is higher. Sex plays a role: women are more likely to develop rheumatoid arthritis, while men are more likely to develop gout.

Excess weight increases stress on weight-bearing joints, speeding up osteoarthritis in knees, hips, and lower back. Previous joint injury — from a sports accident, fall, or workplace injury — raises the risk that osteoarthritis will develop in that joint years later. Repetitive motion in work or hobbies can wear down joints faster; assembly line workers, musicians, and athletes in high-impact sports face higher risk.

Smoking increases the risk of rheumatoid arthritis and may speed up osteoarthritis. Infections can trigger rheumatoid arthritis or other autoimmune forms. Hormonal changes — pregnancy, menopause, or hormone therapy — may influence whether rheumatoid arthritis develops or flares. Having multiple risk factors does not may provide arthritis, but it means paying attention to joint health early on is worthwhile.

How age and wear accumulate over time

Osteoarthritis is often called a "wear and tear" disease, but that phrase can be misleading. It is not straightforward that older joints wear out like old machinery. Instead, the body's ability to repair cartilage damage slows with age. Cartilage has no blood vessels, so it heals slowly even in young people. As you age, the cells that maintain cartilage become less active, and inflammation in joints increases naturally.

This is why osteoarthritis is rare before age 40 but common after 60. It is also why someone who injured a knee at 25 might develop osteoarthritis in that knee by 50, while someone else with no injury history stays pain-free into their 80s. The injury accelerated the wear; the aging process made repair harder.

For rheumatoid arthritis, age works differently. It can start at any age, though it is most common in people over 40. Once it starts, the damage accumulates over time if not treated. This is why early diagnosis and treatment are so important — slowing inflammation early prevents years of joint damage down the road.

Frequently Asked Questions

Can you catch arthritis from someone else?

No, arthritis itself is not contagious. However, some infections can trigger arthritis. For example, untreated Lyme disease can cause joint pain and swelling. If you have been bitten by a tick or have symptoms after an infection, tell your doctor so the infection can be treated before it causes joint damage.

Does arthritis always run in families?

Arthritis does not always run in families, but family history increases your risk. If your parents have osteoarthritis, you are more likely to develop it, but it is not may provide. Lifestyle factors — weight, activity level, previous injuries — also play a large role. Even without family history, arthritis can develop.

Can arthritis develop suddenly or does it always come on slowly?

Osteoarthritis usually develops slowly over years. Rheumatoid arthritis and gout can start suddenly — sometimes overnight. If you wake up with severe joint pain, swelling, or redness, especially in multiple joints or after an infection, see a doctor soon. Early treatment can prevent lasting damage.

Does exercise cause arthritis?

Regular moderate exercise does not cause arthritis and may help prevent it by keeping joints mobile and muscles strong. High-impact sports or repetitive motions done incorrectly over many years can increase wear on joints. The key is balanced activity, proper technique, and rest days — not avoiding movement altogether.

Is arthritis only in older people?

Osteoarthritis is most common in older adults, but rheumatoid arthritis, gout, and other types can develop at any age, including childhood. Young people with joint pain should see a doctor for diagnosis rather than assuming it will go away or that they are too young for arthritis.