Jaundice is a yellow discolouration of the skin and membranes, often most visible in the eye where the white becomes yellow.
The condition is very common in newborn babies - more than 60 per cent are affected - but is much rarer in older children in the UK. In adults it's usually the sign of an underlying problem, such as liver damage.
What causes it?
Jaundice is caused by the build-up of a pigment called bilirubin, produced when the body breaks down red blood cells at the end of their lifespan. The liver usually deals with bilirubin by incorporating it into bile, which it exports to the gall bladder until it's needed as part of our digestive process.
However, if more red blood cells than normal are being broken down - for example, in a condition called haemolytic anaemia, where red blood cells have a shorter lifespan - or if the liver is not functioning properly then an excess of bilirubin will accumulate in the blood.
Jaundice in adults
In adults, jaundice is often a sign that the liver is not functioning properly. Infections such as hepatitis may be responsible, as may the effects of some drugs.
Another common cause of liver cell damage is alcohol abuse.
If nothing is causing excessive production supply of bilirubin and the the liver is not damaged then a problem with excretion (ie removal) of the bile is likely to be responsible.
If the bile can't get out of the liver because of an obstruction, then it collects there and bilirubin is forced back into the blood, causing jaundice. Gallstones are a common cause of this type of obstruction.
Jaundice in children
Jaundice may occur in the very first day of a baby's life because of a problem breaking down old the blood cells. This can have a variety of causes, including rhesus incompatibility and inherited deficiencies in enzymes.
More commonly, however, it develops after two to three days as a result of immaturity of the body's system for dealing with bilirubin (known as physiological jaundice).
As with adults, jaundice can also occur because of infections such as hepatitis or blockages to the bowel or bile duct. Another cause is an underactive thyroid gland.
What are the symptoms?
The main symptom of jaundice is yellowing of the skin and eyes. It tends to start on the head and face and spread down the body. The skin may be itchy.
If the jaundice is severe it can cause brain damage. Signs of this in small babies are sleepiness and poor feeding. In some types of jaundice, the child may pass dark urine and very pale faeces.
How's it diagnosed and treated?
Jaundice is most easily seen if you blanch the skin with pressure - the nose is a good spot. It can be confirmed using a simple blood test.
Treatment depends on the cause. In children, physiological jaundice may settle without treatment but light therapy (phototherapy) may be needed. This exposes the baby to blue band light, which breaks the pigment down into a harmless form.
Side-effects are minor but include rash and diarrhoea.
If bilirubin reaches dangerous levels, a type of blood transfusion called an exchange transfusion may be needed. Antibiotics for infection or antiviral drugs for hepatitis may also be appropriate.
In adults, it's important to identify where the source of the problem lies. Blood tests can check for infection, liver function or excessive breakdown of red blood cells. Scans may also be used to identify whether there's an obstruction or whether the liver's inflamed.
Sometimes a liver biopsy is performed to examine whether it's diseased.