Although there are multiple risk factors involved in the development of hepatitis C, most of them are related to the transmission of hepatitis C virus (HCV). Hepatitis C virus is the main cause of hepatitis C and many other forms of liver disease (hepatic fibrosis, cirrhosis, hepatocellular carcinoma). Hepatitis C is a potentially life-threatening infectious disease, despite its slow-evolving character. In the absence of medical treatment, mild forms of hepatitis C don't usually clear up on their own; in many cases the infection persists, leading to the development of chronic hepatitis C (characterized by frequent recurrence of its symptoms). Furthermore, undiscovered chronic hepatitis C can aggravate over the years, leading to complications such as cirrhosis and even end-stage liver disease.

Statistics indicate that around 170.000.000 people worldwide suffer from chronic liver diseases due to infection with hepatitis C virus. Research results reveal that hepatitis C affects about 150.000 people in the United States each year, many patients with the acute form of the disease developing chronic hepatitis C in time. Hepatitis C virus accounts for around 10.000 annual deaths in the United States alone and it is considered to be the leading cause of death in people with liver disease.

While many species seem to be immune to HCV, this type of virus is the major cause of hepatitis C in humans and certain primates. Hepatitis C virus is known to be the main cause of hepatitis C and several other liver diseases in humans and chimpanzees, triggering similar symptoms in both these species.

Hepatitis C virus can be transmitted through direct contact with contaminated blood or blood products. Also, HCV can be contracted through the use of inadequately sterilized medical utensils such as needles and syringes. Before 1992, the main cause of hepatitis C transmission was the use of contaminated blood transfusions, as there were no effective means of screening the donated blood for viruses at that time. The risk of contracting hepatitis C virus by using blood transfusions has considerably decreased since 1992, as new, improved methods of checking the donated blood for possible infectious agents became available to modern medicine.

Nowadays, potential causes of hepatitis C transmission are: intravenous drug use (sharing needles and syringes with infected people), long-term dialysis, frequent exposure to blood and blood products (health care workers are very exposed to contracting hepatitis C virus), sharing personal items (razors, toothbrushes or hairbrushes) with people infected with hepatitis C.

Less common causes of hepatitis C transmission are: mother to infant infection (prenatal hepatitis C transmission) and unprotected sexual intercourse with an infected person. Although sexual transmission of HCV is rare, hepatitis C can sometimes be acquired through the exchange of body secretions. However, physical contact with an infected person's saliva, sweat or tears can't be considered a cause of hepatitis C transmission.

In many cases, the actual cause of hepatitis C transmission remains unknown. The cause of hepatitis C transmission remains uncertain in around 10 percent of people with acute forms of hepatitis C and in around 20 percent of people with chronic forms of hepatitis C.