Rheumatoid arthritis (RA) is a chronic autoimmune condition that occurs when your immune system mistakenly attacks the healthy tissue that covers your joints.

Researchers aren’t sure what causes a person to develop RA. But there are a few risk factors that have been studied and shown to have a link to RA. Read on to learn more about these risk factors.

Studies have shown that RA appears to run in some families.

People with certain genes that control immune responses seem to be at higher risk for RA. The primary gene connected to RA is the HLA-DR4. You’re five times more likely to develop RA if you have this gene. Other genes include:

  • STAT4
  • TRAF1
  • C5
  • PTPN22

The link appears strongest in identical twins, where one twin has around a 15 percent chance of developing RA if the other twin has the condition. But chances of RA passing from parent to child are much lower, and it’s very common to be the only person in your family with RA.

Research has shown that exposure to smoking or environmental hazards like air pollution or insecticides may increase your chance of developing rheumatoid arthritis.

Smoking shows the strongest link to RA. The risk increases the longer you smoke. Other environmental and lifestyle factors that seem to increase your risk for developing RA include:

Researchers think that hormones are linked to a higher risk of RA.

One reason is that the condition is significantly more common in people assigned female at birth. Additionally, RA often first appears following a hormonal change like those that come with childbirth, breastfeeding, or menopause. This likely means hormones can be a trigger for RA.

Some research suggests that bacteria or viruses might trigger RA. For example, studies have been done to examine the link between periodontal disease and RA.

Researchers believe that the bacterial buildup in periodontal disease can cause your body to produce antibodies. These antibodies can activate an immune system response that can lead to RA.

People often first develop RA following a stressful or traumatic period in their life, physical injury, or illness. It’s unclear why traumas seem to be linked to RA for so many people, and there’s no proven link or research to support the theory that trauma triggers RA. But some studies have investigated this theory.

While no link has been found, there does seem to be an increased risk of RA among some groups, including people with recent severe joint injuries.