Hepatitis C is a liver infection that can lead to serious liver damage. It's caused by the hepatitis C virus. About 3.9 million people in the U.S. have the disease. But it causes few symptoms, so most of them don't know. The virus spreads through an infected person's blood or body fluids. The hepatitis C virus is a small, enveloped, positive-sense single-stranded RNA virus of the family Flaviviridae. The hepatitis C virus is the cause of hepatitis C and some cancers such as liver cancer and lymphomas in humans.