Rheumatoid arthritis happens when your immune system attacks the lining of your joints

Rheumatoid arthritis (RA) is an autoimmune disease, which means your body's immune system mistakenly treats the tissue around your joints as a threat and attacks it. This attack causes inflammation, swelling, and pain. Unlike osteoarthritis, which develops from wear and tear over time, RA can start suddenly and affect multiple joints at once — often both hands, both knees, or both feet in a matching pattern.

The exact reason your immune system turns against your own joints is not fully understood, but researchers have identified several factors that work together to trigger the disease. No single cause explains why one person develops RA and another does not, even in the same family.

Key Takeaways

  • Rheumatoid arthritis is an autoimmune disease in which your immune system attacks the lining of your joints, causing inflammation and pain.
  • Genetics play a role — certain genes make RA more likely, but having those genes does not mean you will develop the disease.
  • Environmental triggers such as smoking, infections, and stress may set up RA in people who are genetically predisposed.
  • Women are two to three times more likely to develop RA than men, and hormones may influence when the disease appears.
  • RA usually develops between ages 30 and 60, though it can start at any age.

Genetics: The inherited risk that does not may provide disease

If a parent or sibling has rheumatoid arthritis, your risk is higher than the general population. Researchers have found that certain genes — particularly one called HLA-DR4 — appear more often in people with RA. However, many people carry these genes and never develop the disease, and some people without these genes do develop RA.

Genetics loads the gun, but something else has to pull the trigger. Scientists believe that a person needs both the genetic predisposition and an environmental event — an infection, an injury, or prolonged stress — for RA to actually begin. This is why RA often runs in families but skips generations or affects only some siblings.

Infections and the immune system's mistaken identity

Several infections have been studied as possible triggers for RA. The most researched is Epstein-Barr virus (EBV), the virus that causes mononucleosis. Some people who develop RA have had EBV, though most people who have had EBV never develop RA. Other infections under investigation include parvovirus B19 and certain bacteria in the gut.

The theory is that the immune system fights off the infection, but in genetically vulnerable people, it continues attacking even after the infection is gone — and the target shifts to joint tissue that resembles the virus. This is called molecular mimicry. The infection itself may have passed months or years before RA symptoms appear.

Smoking: A major environmental risk factor

Smoking is one of the strongest environmental risk factors for developing rheumatoid arthritis. People who smoke are significantly more likely to develop RA than people who have never smoked. The risk is even higher in people who smoke and carry the genetic risk genes.

Smoking appears to damage the lining of the lungs in a way that triggers an immune response. That response may then spread to the joints. Former smokers still have an elevated risk compared to people who never smoked, though the risk decreases over time after quitting.

Hormones and why women are more often affected

Women develop rheumatoid arthritis two to three times more often than men. Hormones are thought to play a role. RA often starts or worsens during times of hormonal change — after pregnancy, during perimenopause, or when starting certain medications.

Estrogen may influence how the immune system works. Some research suggests that low estrogen levels increase the risk of RA, while other studies point to how estrogen interacts with immune cells. Pregnancy sometimes improves RA symptoms temporarily, possibly because of hormonal shifts, but symptoms often return after delivery.

Stress, injury, and other possible triggers

Prolonged physical or emotional stress may set up RA in people who are genetically predisposed. A major life event, chronic work stress, or a serious illness can precede the onset of symptoms by weeks or months. Joint injury has also been studied as a possible trigger — some people report that RA started in a joint they had injured years earlier.

Obesity may increase RA risk as well. Fat tissue produces inflammatory chemicals that may contribute to the autoimmune attack. Weight loss has been shown to reduce RA symptoms in some people, though it does not reverse the disease.

Why RA usually appears between ages 30 and 60

Rheumatoid arthritis most commonly develops in middle age, though it can start at any age. Children can develop juvenile idiopathic arthritis (a related but distinct condition), and older adults can develop RA for the first time. The reason RA clusters in the 30–60 age range is not entirely clear, but it likely reflects the time it takes for multiple triggers to align — genetic predisposition plus an environmental event plus enough time for the immune system to develop antibodies against joint tissue.

The longer you live, the more infections you have been exposed to and the more cumulative stress your body has experienced. This may explain why middle age is when RA most often appears.

What RA is not: Common misconceptions

Rheumatoid arthritis is not caused by cold weather, though cold can make symptoms worse. It is not caused by diet alone, though certain foods may worsen inflammation in people who already have RA. It is not contagious, and you cannot catch it from someone else.

RA is also not the same as osteoarthritis, which develops from joint wear and tear and is not an autoimmune disease. The two conditions can occur in the same person, but they have different causes and require different treatment approaches.

Frequently Asked Questions

Can you develop rheumatoid arthritis at any age?

RA most commonly starts between ages 30 and 60, but it can develop at any age. Children can develop juvenile idiopathic arthritis, and older adults can develop RA for the first time. Age alone does not prevent RA from starting.

If my parent has rheumatoid arthritis, will I definitely get it?

No. Having a parent with RA increases your risk, but most people with a family history of RA never develop it. You would need both the genetic predisposition and an environmental trigger — such as an infection or prolonged stress — for RA to actually begin.

Does stress cause rheumatoid arthritis?

Stress alone does not cause RA, but prolonged emotional or physical stress may trigger it in people who are genetically predisposed. Stress appears to be one piece of a larger puzzle that includes genes, infections, and other environmental factors.

Can you prevent rheumatoid arthritis if it runs in your family?

There is no proven way to prevent RA, but you can reduce some risk factors. Quitting smoking is the strongest step you can take. Managing stress, maintaining a healthy weight, and treating infections promptly may also lower your risk, though they do not may provide prevention.

Does diet cause rheumatoid arthritis?

Diet does not cause RA, but certain foods may worsen inflammation in people who already have the disease. RA is triggered by a combination of genetics and environmental factors, not by what you eat. However, an anti-inflammatory diet may help manage symptoms once RA has developed.