Nonalcoholic steatohepatitis (NASH) is liver inflammation and damage caused by a buildup of fat in the liver.It is part of a group of conditions called nonalcoholic fatty liver disease.You may be told you have a fatty liver..ASH can get worse and cause scarring of the liver, which leads to cirrhosis. But the disease doesn't always get worse. NASH is similar to the kind of liver disease that is caused by long-term, heavy drinking.