Primary biliary cirrhosis - Causes of primary biliary cirrhosis

The exact cause of primary biliary cirrhosis (PBC) is unknown, although it is widely thought to be the result of a problem with the immune system.

Autoimmune condition

Most experts believe that PBC is an autoimmune condition. This means that something goes wrong with the immune system (the body's natural defence against infection and illness) and it attacks healthy tissue instead of fighting off infection.

In cases of PBC, the immune system sends specialised cells that usually kill bacteria and viruses to the bile ducts.

These cells damage the surface of the bile ducts, which gradually become scarred and disrupt the flow of bile out of the liver. This increases the amount of bile in the liver, which over time can cause it to also become extensively damaged and scarred (cirrhosis).

This damage can gradually cause the liver to lose its function. As the liver plays a vital role in filtering out impurities and toxins from your blood, loss of liver function is potentially fatal.

It is not known what causes the immune system to malfunction and attack the bile ducts.

Other autoimmune conditions

People with PBC are often more likely to also have another autoimmune condition. For example, they may also have:

• an underactive thyroid (hypothyroidism) – where the thyroid gland does not produce enough hormones
• rheumatoid arthritis – a condition that causes pain and swelling in the joints 
• scleroderma – a condition that affects connective tissue (the supporting tissues of the body), causing hard, puffy and itchy skin
• autoimmune hepatitis – a very rare cause of long-term hepatitis, where the immune system attacks the liver
• Sjögren's syndrome – a condition in which the immune system attacks the body's tear and saliva glands
• Raynaud's phenomenon – a common condition that affects the blood supply to certain parts of the body, usually the fingers and toes
• coeliac disease – a common digestive condition where a person has an adverse reaction to gluten because the immune system mistakes substances found inside gluten as a threat to the body

Increased risk

Although the reason why some people develop PBC is not clear, it's thought that your genes may make you more susceptible to developing the condition and that it is triggered by something else.

There is some evidence to suggest that certain things can increase your chances of developing PBC. These are explained below.

Gender

PBC occurs mostly in women. Less than one in 10 cases of PBC occur in men.

One theory for this is that the immune system may be affected by the female sex hormone, oestrogen.

Family history

Having a close relative with PBC means you are more likely to develop the condition yourself.

For example, if you are female and your mother has or has had PBC, you are much more likely to develop PBC than someone who has no relatives with the condition. However, the risk is still low.

Possible triggers

Certain things may trigger PBC in people with a genetic tendency. These include:

• infections – such as a urinary tract infection (UTI)
• hormone replacement therapy (HRT) – a treatment used to replace the female hormones that a woman's body no longer produces because of the menopause
• using nail varnish or cosmetics 
• smoking cigarettes or having a history of heavy smoking
• living near to where toxic waste has been dumped

However, none of these have been proven as definite triggers of PBC. Most people who are exposed to them will not develop the condition. There is nothing to suggest that you should reduce your exposure to these triggers to lower your risk of developing PBC.