Lactose is made up of :

Lactose, commonly referred to as milk sugar, is a disaccharide found in the milk of mammals [1]. Chemically, it is composed of two monosaccharide units: D-glucose and D-galactose [2]. These two sugar fragments are joined together by a specific glycosidic linkage, specifically a beta-1,4-glycosidic bond [2]. In the human digestive system, the enzyme lactase is responsible for hydrolyzing lactose back into its constituent monosaccharides, glucose and galactose, for absorption into the bloodstream. This distinguishes it from other common disaccharides like sucrose, which consists of glucose and fructose, or maltose, which is made of two glucose molecules [1]. While glucose and galactose share the same chemical formula (C6H12O6), they are structural isomers with different arrangements of functional groups.

Sources

1. [1] https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_31_02.html
2. [2] https://pubchem.ncbi.nlm.nih.gov/compound/LACTOSE