It’s not known exactly what causes reactive arthritis, but it is thought to be the result of the immune system reacting to a previous infection.

The immune system

Your immune system is your body’s defence against illness and infection. When it senses the presence of an infectious agent, such as a virus or bacteria, it will send antibodies and cells to fight the infection.

These antibodies then release chemicals that cause nearby tissues to swell and become filled with fluid. This process is known as inflammation.

Inflammation makes it harder for the infection to spread and can allow the body to kill the bacteria or virus responsible for the infection.

In cases of reactive arthritis, something goes wrong with the immune system and it acts like there’s still an infection in the body, even though the previous infection has passed.

Infection

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

• sexually transmitted infections (STIs) – such as chlamydia or gonorrhoea , although many cases occur after non-gonococcal urethritis
• infections of the bowel and digestive system (gastrointestinal infections) – usually caused by two types of bacteria called campylobacter and salmonella, both of which can cause food poisoning

Genetic factors

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

In the UK, it’s estimated that around one in 10 people have the HLA-B27 gene. Three out of four cases of reactive arthritis develop in people with the HLA-B27 gene. They tend to have more severe symptoms, with a greater risk of their symptoms reoccurring.

One study found that people with the HLA-B27 gene had around a one in 50 chance of developing reactive arthritis after contracting a stomach or digestive infection. It’s unclear whether there’s a similar risk after contracting a STI.

Exactly how HLA-B27 contributes to the development of reactive arthritis is unclear, although research is ongoing.

Reactive arthritis is a condition that causes inflammation (redness and swelling) in various places in the body.

It usually develops following an infection, and in most cases clears up without causing future problems.

The three most common places affected by reactive arthritis are:

• the joints (arthritis), which can cause symptoms such as pain and stiffness
• the eyes (conjunctivitis), which can cause symptoms such as eye pain and redness of the eyes
• the urethra (urethritis), which can cause pain when urinating (the urethra is the tube that carries urine out of the body) 

Read more about the symptoms of reactive arthritis.

Seeking medical help

It’s recommended you contact your GP if you have any swollen and painful joints, especially if you have recently had diarrhoea or problems passing urine.

Causes

Reactive arthritis develops after an infection, typically after a sexually transmitted infection (STI) such as chlamydia, or an infection of the digestive system.

For reasons that are still unclear, two to four weeks after the infection has passed the immune system (the body’s defence against infection) appears to malfunction and starts attacking healthy tissue, causing it to become inflamed. 

Read more about the causes of reactive arthritis.

Diagnosis and treatment

There is no single test for reactive arthritis, although blood tests and X-rays may be used to rule out other causes of your symptoms. An assessment of your symptoms and recent medical history – such as whether you may have recently had a digestive or sexually transmitted infection – should help lead to a diagnosis.

There is currently no cure for reactive arthritis, but the condition usually improves after three to 12 months. Meanwhile, treatment can help relieve symptoms such as pain and stiffness.

Mild to moderate symptoms can usually be controlled using non-steroidal anti-inflammatory drugs (NSAIDs) painkillers, such as ibuprofen.

More severe symptoms will usually require steroid medication (corticosteroids) or disease-modifying anti-rheumatic drugs (DMARDs).

Read more about the treating reactive arthritis.

Who is affected?

Reactive arthritis is a relatively uncommon condition. It is estimated that one in every 2,500 people will develop a new case of reactive arthritis in any given year in the UK.

Reactive arthritis that occurs after a digestive infection affects men and women equally.

Reactive arthritis that occurs after a sexually transmitted infection is much more common in men, who account for nine out of 10 cases.

Most cases of reactive arthritis develop in people who are 20-40 years of age, although it can affect children.

The most effective way to prevent reactive arthritis is to avoid the most common infectious causes of the condition.

These are:

• sexually transmitted infections (STIs) 
• infections of the bowel and digestive system (gastrointestinal infections)

Contraception

The most effective way of preventing STIs is to always use a barrier method of contraception, such as a condom, during sexual intercourse. This includes both anal and oral sex.

This greatly reduces your risk of getting STIs, such as chlamydia and gonorrhoea, which are the main types of STIs that can lead to reactive arthritis. The male condom is the most effective type of contraception to prevent STIs.

For more advice, see STIs, condoms and sexual health.

Good hygiene

Ensuring good standards of hygiene when preparing and storing food can help prevent gastrointestinal infections.

Following the advice below will help lower your risk of infection:

• Wash your hands thoroughly with soap and hot water and dry them before handling food. Also wash them after handling raw meat, going to the toilet, blowing your nose or handling animals (including pets).
• Before starting to prepare food, wash work surfaces thoroughly, particularly after they’ve been touched by raw meat (including poultry) or raw eggs. Also clean them after you’ve finished preparing food.
• Use separate chopping boards for raw meat and ready-to-eat food.
• Keep raw meat away from ready-to-eat foods, such as salad, fruit and bread.
• Cook food thoroughly. Before eating, check it’s piping hot all the way through.
• Keep your fridge temperature between 0-5ºC (31.9-40.9ºF). Keeping food cold will prevent bacteria growing.
• Avoid eating food that’s past its use-by date.
• When travelling in areas where gastrointestinal illnesses are common, take care to avoid unwashed fruit and vegetables, and ensure you only use clean water for drinking, cleaning your teeth and washing food.

Read more about food safety and preventing food poisoning.

The symptoms of reactive arthritis usually develop two to four weeks after an infection.

In most cases, reactive arthritis follows a sexually transmitted infection (STI) such as chlamydia, or a digestive infection such as food poisoning.

The three parts of the body most commonly affected by reactive arthritis are:

• the joints and tendons
• the urinary system
• the eyes

Joints and tendons

Reactive arthritis usually involves inflammation of the joints (arthritis) and tendons, which can cause symptoms of:

• joint pain and swelling, usually in weight-bearing joints such as your knees, ankles and hips
• lower back and buttock pain
• heel pain
• swelling of your fingers and toes

The urinary system

Reactive arthritis can sometimes also cause inflammation of the urethra (urethritis), which is the tube that carries urine out of the body. Symptoms of urethritis include:

• pain or a burning sensation during urination
• urinating more often than usual
• having a sudden urge to urinate
• a discharge of fluid from the penis or vagina
• blood in your urine (less commonly)

The eyes

Reactive arthritis may also cause inflammation of the eyes (conjunctivitis). Symptoms of conjunctivitis include:

• reddening of the eyes
• watery eyes
• eye pain
• swollen eye lids

In rare cases, a type of uveitis called iritis can occur. Eyes affected by iritis can be painful, red and sensitive to light. If you have these symptoms, you should see your doctor or an eye specialist as soon as possible.

Other symptoms of reactive arthritis

Reactive arthritis can also cause several other symptoms, including:

• feeling unusually tired (fatigue)
• mild fever (a high temperature between 37-38°C or 98.6-101.0°F)
• mouth ulcers
• painless white rashes inside your mouth
• a skin rash
• your nails can become thick and crumbly
• abdominal pain
• bouts of diarrhoea

When to seek medical advice

It’s recommended you contact your GP if you have any swollen and painful joints, especially if you have recently had diarrhoea or problems passing urine.

There’s no cure for reactive arthritis, but the condition is usually temporary and treatment can help relieve your symptoms.

Self care

In the initial stages of reactive arthritis, it’s recommended you get plenty of rest and avoid using affected joints.

As your symptoms improve, you should begin a gradual programme of exercise designed to strengthen affected muscles and improve the range of movement in your affected joints.

Your GP or specialist may recommend a suitable exercise programme for your arthritis. Alternatively, you may be referred to a physiotherapist for physical therapy. 

You might also find ice packs and heat pads useful in reducing joint pain and swelling, although these should not be directly placed on your skin. Instead, you should cover them – for example, with a towel.

Non-steroidal anti-inflammatory drugs (NSAIDs)

Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, are the first type of medication used for reactive arthritis as they can help reduce inflammation and relieve pain.

Taking a regular dose of an NSAID on a long-term basis can increase your risk of getting stomach ulcers or bleeding. If you are at an increased risk of developing stomach ulcers, your GP may recommend an additional medication known as a proton pump inhibitor, which reduces the production of stomach acid.

Long-term use of NSAIDs may also slightly increase your risk of having a heart attack or stroke.

Steroid medications

Steroid medication (corticosteroids) may be recommended if your symptoms don’t respond to NSAIDs or you’re unable to use NSAIDs, for example because you have a history of stomach ulcers.

Steroids work by blocking the effects of many of the chemicals that the body uses to trigger inflammation.

A corticosteroid called prednisolone is usually the preferred choice. Prednisolone can be given as an injection into a joint or as a tablet.

Your dose will gradually be reduced over a period of weeks, depending on how well you respond to treatment.

Never stop taking your steroid medicines, unless you’re told by your doctor that it’s safe to do so. Suddenly stopping treatment with steroids can make you feel very ill.

Side effects

About one in 20 people who take prednisolone will experience changes in their mental state, such as depression or hallucinations. Contact your GP as soon as possible if you notice any change.

Other side effects include weight gain, acne, stomach ulcers and osteoporosis, although these should improve as your dosage is decreased.

If you’re over 65, your GP may also prescribe medication to strengthen your bones to avoid the effects of osteoporosis (see treating osteoporosis for more information).

You may also be referred for a type of X-ray known as a dual-energy X-ray absorptiometry (DEXA) scan, which can be used to assess how strong your bones are.

As with NSAIDs, stomach ulcers can also be a problem for people taking prednisolone on a long-term basis, so you may also be prescribed a proton pump inhibitor.

Disease-modifying anti-rheumatic drugs (DMARDs)

If your symptoms persist despite treatment with NSAIDs and/or corticosteroids, you may be prescribed a medication known as a disease-modifying anti-rheumatic drug (DMARD).

DMARDs also block the effects of some of the chemicals that your immune system uses to trigger inflammation.

It can take four to six months before you notice a DMARD working, so it’s important to keep taking medication even if you don’t see immediate results.

A DMARD called sulfasalazine is usually the preferred option. Common side effects of sulfasalazine include feeling sick, loss of appetite and headaches, although these usually improve once your body gets used to the medication. 

DMARDs may also cause changes in your blood or liver, so it is essential to have regular blood tests while taking these medicines.