Reactive arthritis

Also called Reiter's syndrome

Reactive arthritis is a condition that causes pain and swelling in the joints, usually within 4 weeks of an infection. The infection is often a sexually transmitted infection, such as chlamydia, or a gut infection, such as food poisoning. It mostly affects people aged 20 to 40 and often affects the knees, ankles and feet.

Last updated Nov 9, 2026

What it is

Most people get better within a year. Some have symptoms that come back.

Treatment includes anti-inflammatory medicines, steroid injections, and antibiotics if the infection is still present. Physiotherapy can help joints recover.

Common signs

  • Painful, swollen joints, often in the legs
  • Pain in the heels or tendons
  • Sore, red eyes
  • Pain when peeing
  • Lower back pain
  • Tiredness or a mild fever

How it is usually diagnosed

  • Questions about recent infections
  • Blood and urine tests
  • Swabs for sexually transmitted infections
  • Sometimes fluid taken from the joint

Records worth keeping

Keeping these together makes each appointment easier, especially when you see a new doctor:

  • Blood, urine and swab results
  • Rheumatology letters
  • Prescriptions

Questions to ask your doctor

  • Which infection triggered this?
  • Does my partner need testing?
  • What can I do if it comes back?

When to get help right away

Call 112 or go to the nearest emergency department if you have:

  • A single hot, red, very painful joint with a fever, or a red painful eye with vision changes: get urgent help the same day

This page is general information. It is not a diagnosis and does not replace a doctor who knows your history. Medfold keeps your records organised; it does not interpret them.

Sources