Cholestasis in infants is a common disease in infancy, caused by a variety of etiologies, and its pathogenesis and diagnostic ideas are described below. I. What is infantile cholestasis? Bile is an important digestive fluid in the body. Bile is produced by liver cells, secreted through the bile duct system and finally discharged into the duodenum to help digestion and absorption of fat. Due to various reasons, bile production, secretion or poor flow in the bile duct system, not all the bile is discharged into the small intestine, and it accumulates in the liver and bile, which is called cholestasis. If it occurs in infants (including newborns), it is called infantile cholestasis. The cholestasis is divided into: 1. hepatocellular cholestasis; 2. biliary cholestasis; (1) intrahepatic biliary cholestasis; (2) extrahepatic biliary cholestasis; 3. mixed cholestasis. Its typical clinical manifestations are jaundice, pruritus, fecal and urine color changes and blood biochemical abnormalities. All the non-conjugated bilirubin produced by human red blood cells after aging must be transformed into conjugated bilirubin by the action of hepatocytes, however, it is excreted out of the body through feces and urine. After bile accumulation, the amount of conjugated bilirubin excreted in the feces through the intestinal tract is reduced or absent, making the feces lighter in color or clay-colored. On the contrary, the bilirubin excreted in the urine increases, making the urine darker, dark yellow or brown. On the other hand, the liver’s ability to convert bilirubin is reduced after biliary stasis, so the amount of both total and conjugated bilirubin in the blood increases, producing jaundice. In addition, bile sludge increases the synthesis of opioid peptides in the liver, which leak into the circulation and act on the central nervous system and opioid receptors in the skin causing pruritus. Also, bile salts continue to be a cause of skin irritation causing pruritus. Itching rarely occurs in infants, probably due to lack of neurosensitivity, even if bile is stagnant. In addition to increased values of total bilirubin and conjugated bilirubin, there are also increased values of total bile acids and γ-glutamyl transaminase (γ-GT) in the blood biochemistry. What is biliary liver disease in infants? Biliary liver disease is called cholestatic liver disease, which has both symptoms of cholestasis and liver disease. The latter manifests as hepatocellular lesions and the resulting pathological liver signs: a liver larger than 2.0-2.5 cm in size and/or a hardened liver in the right midclavicular line of the infant; and increased blood alanine aminotransferase (ALT) or aspartate aminotransferase (AST). The etiology is twofold: (1) causative factors involving both the biliary system and hepatocytes, such as CMV hepatitis; (2) secondary hepatocellular damage due to biliary stasis, such as biliary cirrhosis secondary to congenital extrahepatic biliary atresia in most children 2-3 months later.