For reasons that are still unclear, the immune system (the body's defence against infection) overreacts in response to an infection and starts attacking healthy tissue in the joints, causing them to become inflamed.
You can't catch reactive arthritis from another person. Only very few people who get gut or genital infections will get reactive arthritis.
Who is affected
- Reactive arthritis is most common in men 20–40 years old.
- People born with the HLA-B27 gene are more likely to get reactive arthritis.
- People who have had a sexually transmitted infection (STI) such as chlamydia or gonorrhoea. In men, the STI usually has symptoms. In women, the STI may have no symptoms but they can still develop reactive arthritis.
- People with HIV.
- People who have had food poisoning, even very mildly.