Lactose is a
disaccharide sugar derived from
galactose and
glucose that is found in
milk. Lactose makes up around 2–8% of milk (by weight), although the amount varies among species and individuals, and milk with a reduced amount of lactose also exists. It is extracted from sweet or sour
whey. The name comes from or , the
Latin word for milk, plus the
-ose ending used to name sugars. It has a formula of C
12H
22O
11 and the hydrate formula C
12·11H
2O, making it an
isomer of
sucrose.