One of the most important organs in the body, the liver eliminates toxins, stores energy and manufactures essential substances such as body-building proteins and blood-clotting factors. In good health, it is a resilient organ, capable of remarkable regeneration. The liver's vital functions mean that disease is usually serious and often life-threatening. Viruses, poisoning by drugs or alcohol and autoimmune reactions can cause inflammation (hepatitis), and cirrhosis (scarring). Hepatitis caused by viral infections affects millions of people worldwide. Chronic infection leads to liver failure, cirrhosis and an increased risk of liver cancer.