In many cases, the exact cause of restless legs syndrome is unknown.

When no cause can be found, it's known as idiopathic or primary restless legs syndrome.

Research has identified specific genes related to restless legs syndrome, and it can run in families. In these cases, symptoms usually occur before the age of 40.

There's evidence to suggest restless legs syndrome is related to a problem with part of the brain called the basal ganglia.

The basal ganglia uses a chemical (neurotransmitter) called dopamine to help control muscle activity and movement.

Dopamine acts as a messenger between the brain and nervous system to help the brain regulate and co-ordinate movement.

If nerve cells become damaged, the amount of dopamine in the brain is reduced, which causes muscle spasms and involuntary movements.

Dopamine levels naturally fall towards the end of the day, which may explain why the symptoms of restless legs syndrome are often worse in the evening and during the night.

Restless legs syndrome can sometimes occur as a complication of another health condition, or it can be the result of another health-related factor.

This is known as secondary restless legs syndrome.

You can develop secondary restless legs syndrome if you:

• have iron deficiency anaemia (low levels of iron in the blood can lead to a fall in dopamine, triggering restless legs syndrome)
• have a long-term health condition (such as chronic kidney disease, diabetes, Parkinson's disease, rheumatoid arthritis, an underactive thyroid, or fibromyalgia)
• are pregnant (particularly from week 27 until birth; in most cases the symptoms disappear within 4 weeks of giving birth)

There are a number of triggers that don't cause restless legs syndrome, but can make symptoms worse.

These include medications such as:

• antidepressants
• some antipsychotics
• lithium (used in the treatment of bipolar disorder)
• antihistamines

Other possible triggers include:

• excessive caffeine or alcohol
• smoking
• being overweight or obese
• stress