The most common forms are Hepatitis A , Hepatitis B and Hepatitis C. Most cases of Hepatitis are caused by viruses . Hepatitis is acute when it lasts less than six months and chronic when it persists longer . A group of viruses known as the hepatitis viruses cause most cases of hepatitis worldwide , but it can also be due to toxins ( notably alcohol , certain medications , some industrial organic solvents and plants ) , other infections and autoimmune diseases .