Rheumatoid arthritis develops when your immune system attacks the lining of your joints, but scientists still don't fully understand why this happens in some people and not others

Rheumatoid arthritis (RA) is an autoimmune disease, meaning your body's immune system mistakenly treats the tissue lining your joints as a threat and attacks it. This causes inflammation, pain, and eventually joint damage. Unlike osteoarthritis, which comes from wear and tear, RA can start suddenly and affect multiple joints at once—often both hands, both knees, or both feet symmetrically.

The exact trigger for RA remains unknown. Researchers have identified several factors that appear to increase risk, but having those factors does not may provide you will develop the disease. Some people carry genetic markers associated with RA their entire lives and never get it. Others develop it without any known family history. This uncertainty is frustrating for people trying to understand their diagnosis, but it reflects how complex autoimmune diseases actually are.

Key Takeaways

  • Rheumatoid arthritis occurs when your immune system attacks joint linings, not from normal wear and tear like osteoarthritis.
  • Genetics play a role—certain genes increase risk—but genes alone do not cause RA; environmental triggers appear necessary too.
  • Infections, smoking, and hormonal changes are suspected environmental factors, but no single cause has been proven.
  • RA typically appears between ages 30 and 60, though it can develop at any age, and women are diagnosed roughly three times more often than men.
  • Early symptoms include joint pain and swelling that lasts more than six weeks, morning stiffness lasting over an hour, and fatigue.

The genetic component: inherited risk, not inherited disease

If a parent or sibling has RA, your risk is higher than the general population's. The strongest genetic link involves a gene called HLA-DR4 (and related variants). People carrying this gene are more likely to develop RA if exposed to the right environmental trigger. However, roughly 60 percent of people with RA do not carry this gene, and many people who do carry it never develop the disease.

Genetic testing for RA risk is not routine and would not change your current care. The test exists mainly for research. What matters clinically is that if you have a family member with RA, you should mention it to your doctor, especially if you develop joint symptoms. Your doctor may test for specific antibodies (rheumatoid factor or anti-CCP) earlier than they otherwise would, which can catch RA sooner.

Environmental triggers: infections, smoking, and hormonal factors

Scientists suspect that RA develops when a genetically vulnerable person encounters an environmental trigger. The leading candidates are infections—particularly viral infections like Epstein-Barr virus—though no single infection has been proven to cause RA. The theory is that the immune system, while fighting the infection, becomes confused and begins attacking joint tissue even after the infection clears.

Smoking is one of the few environmental factors with strong evidence. People who smoke are roughly twice as likely to develop RA as non-smokers, and the risk increases with how much and how long someone smokes. Quitting reduces the risk over time. Obesity may also increase risk, possibly because fat tissue produces inflammatory chemicals.

Hormonal changes appear relevant too. RA is diagnosed in women three times more often than men, and some women notice symptoms starting or worsening after pregnancy or around menopause. Oral contraceptives may lower risk slightly. These patterns suggest estrogen plays a role, though the mechanism is not yet clear.

Why symptoms appear suddenly even though the process takes time

RA does not develop overnight, even though it often feels that way. The immune system likely begins attacking joint tissue months or even years before a person notices symptoms. Blood tests can detect antibodies (rheumatoid factor or anti-CCP) in people who have no symptoms yet—sometimes years before joint pain appears. This is called seronegative RA when antibodies are absent, or seropositive RA when they are present.

The reason symptoms seem to arrive suddenly is that inflammation builds silently until it reaches a threshold where pain and swelling become noticeable. Once that happens, the damage accelerates. This is why early detection matters: catching RA in the first weeks or months after symptoms start, before significant joint damage occurs, leads to better long-term outcomes.

Age and sex: who develops RA and when

RA can develop at any age, but it most commonly appears between ages 30 and 60. Women are diagnosed roughly three times more often than men. In people over 65, the sex difference narrows somewhat, and men who develop RA after 60 tend to have more aggressive disease.

Juvenile idiopathic arthritis (JIA) is a related but distinct autoimmune arthritis that affects children. It has different causes, different antibody patterns, and different long-term outcomes than adult RA. If a child develops joint symptoms, they need evaluation by a pediatric rheumatologist rather than an adult specialist.

What happens in your joints when RA develops

Your joints are lined with a thin membrane called the synovium. In RA, immune cells attack this lining, causing it to swell and produce excess fluid. The inflamed tissue releases chemicals that damage cartilage and bone. Over months or years without treatment, this can permanently deform joints and limit movement.

The inflammation is not limited to joints. RA can affect the lungs, heart, eyes, and blood vessels. This is why rheumatologists monitor for these complications and why treating the underlying inflammation early matters for your whole body, not just your joints.

Why some people develop RA and others don't

The most honest answer is that we do not yet know. Having a genetic risk factor and exposure to a suspected trigger (like smoking or an infection) still does not may provide RA will develop. Some people have both and never get the disease. Others develop RA without any obvious risk factor.

This gap in understanding is why RA cannot currently be prevented, even if you know you are at higher risk. If you have a family history of RA, the most evidence-based steps are to avoid smoking, maintain a healthy weight, and report any new joint symptoms to your doctor promptly. These actions reduce risk or improve outcomes, but they do not eliminate the possibility of developing RA.

Frequently Asked Questions

Can you catch rheumatoid arthritis from someone else?

No. RA is not contagious. It is an autoimmune disease, meaning your own immune system causes it. You cannot catch it from a family member, coworker, or anyone else, even if you live with someone who has RA.

Does stress cause rheumatoid arthritis?

Stress does not cause RA, but it may worsen symptoms in people who already have it. Some people notice flares during stressful periods. Managing stress through sleep, exercise, and relaxation can help reduce flares, but it cannot prevent RA from developing in the first place.

If my parent has RA, will I definitely get it?

No. Having a parent with RA increases your risk, but most children of people with RA never develop it. Genetics is one piece; environmental triggers appear necessary too. You cannot inherit RA the way you inherit eye color.

Can diet cause rheumatoid arthritis?

Diet alone does not cause RA. However, being overweight may increase risk slightly, and some research suggests certain dietary patterns might influence inflammation in people who already have RA. If you have RA, your doctor or a dietitian can discuss foods that may help manage symptoms.

What is the difference between rheumatoid arthritis and osteoarthritis?

Osteoarthritis comes from wear and tear on joints over time and is not autoimmune. RA is an autoimmune disease that can develop suddenly and affects multiple joints symmetrically. RA typically causes morning stiffness lasting over an hour; osteoarthritis stiffness usually improves within 30 minutes of movement.