Causes of reactive arthritis 

It's not known exactly what causes reactive arthritis, but it's thought to be the result of the immune system reacting to an infection.

The immune system

Your immune system is your body's defence against illness and infection. When it senses a virus or bacteria, it sends antibodies and cells to fight the infection. This causes tissues to swell, known as inflammation, which makes it harder for the infection to spread.  

In cases of reactive arthritis, something goes wrong with the immune system and it causes inflammation in parts of the body that were not infected, often after the infection has already passed.

Infection

The two most common types of infection linked to reactive arthritis are:

Genetic factors

Research has shown that people with a specific gene known as HLA-B27 have a significantly increased chance of developing reactive arthritis, as well as related conditions such as ankylosing spondylitis (a type of arthritis that affects the spine).

In the UK, it's estimated that around 1 in every 10 people have the HLA-B27 gene. Around 3 out of every 4 cases of reactive arthritis develop in people with the gene.

People with the HLA-B27 gene also tend to have more severe and longer-lasting symptoms, with a greater risk of their symptoms recurring.

Exactly how the gene contributes to the development of reactive arthritis is unclear.

Page last reviewed: 08/01/2015

Next review due: 01/01/2018