Introduction 

Chronic fatigue syndrome (CFS) causes persistent fatigue (exhaustion) that affects everyday life and doesn't go away with sleep or rest. 

CFS is also known as ME, which stands for myalgic encephalomyelitis. There's some debate over the correct term to use for the condition, but these pages will refer to the condition as CFS.

CFS is a serious condition that can cause long-term illness and disability, but many people – particularly children and young people – improve over time.

Who is affected?

It's estimated around 250,000 people in the UK have CFS.

Anyone can get the condition, although it's more common in women than men.

It usually develops when people are in their early 20s to mid-40s. Children can also be affected, usually between the ages of 13 and 15. 

How it affects quality of life

Most cases of CFS are mild or moderate, but up to one in four people with CFS have severe symptoms. These are defined as follows: 

  • mild – you're able to care for yourself, but may need days off work to rest
  • moderate – you may have reduced mobility, and your symptoms can vary; you may also have disturbed sleep patterns and need to sleep in the afternoon
  • severe – you're able to carry out minimal daily tasks, such as brushing your teeth, but have significantly reduced mobility, and may also have difficulty concentrating

Read more about the symptoms of CFS.

Why it happens

It's not known exactly what causes CFS. Various theories have been suggested, including:

  • a viral or bacterial infection
  • problems with the immune system
  • an imbalance of hormones
  • psychiatric problems, such as stress and emotional trauma

Some people are thought to be more susceptible to the condition because of their genes, as the condition is more common in some families.

More research is needed to confirm exactly what causes the condition.

Read more about the causes of CFS.

How it is diagnosed

There are specific guidelines issued by the National Institute for Health and Care Excellence (NICE) about the diagnosis and management of CFS.

NICE says a diagnosis of CFS should be considered if you meet specific criteria regarding your fatigue – for example, it can't be explained by other conditions – and if you also have other symptoms, such as sleeping problems or problems thinking and concentrating.

The diagnosis can then be confirmed if these symptoms are experienced for several months.

Read more about diagnosing CFS.

How it is treated

Treatment for CFS may be able to reduce the symptoms. Everyone with CFS responds to treatment differently, so your treatment plan will be tailored to you.

Some of the main treatments include:

Most people with CFS improve over time, although some people don't make a full recovery. It's also likely there will be periods when symptoms get better or worse. Children and young people with CFS are more likely to recover fully.

Read more about treating CFS.

Different terms for the condition

  • chronic fatigue syndrome – often used and preferred by doctors as there's little evidence of brain and spinal cord inflammation, which the term ME suggests; ME is also thought to be too specific to cover all the symptoms of the condition
  • myalgic encephalomyelitis (ME) – preferred by those who feel CFS is not specific enough and doesn't reflect the severity and different types of fatigue, and implies that fatigue is the only symptom (myalgic encephalopathy is sometimes also used)
  • systemic exertion intolerance disease (SEID) – a new term suggested in a 2015 report by the US Institute of Medicine, which implies that the condition affects many systems in the body (systemic); the word "disease" highlights the serious nature of the condition in some people

Page last reviewed: 25/02/2015

Next review due: 25/02/2017