Light micrograph of lactose monohydrate (milk sugar or saccharum lactis) crystals, a disaccharide that is found in human and cow milk. Its biosynthesis takes place in the mammary glands. It is the first and only carbohydrate every newborn mammal consumes in significant amounts. The intestinal villi secrete the enzyme lactase to digest it. In most mammals the production of lactase gradually decreases with age. Lactose intolerance is the inability to digest lactose, due to a lactase deficiency in the digestive system. Some fermenting bacteria convert lactose into lactic acid, the basis for several dairy products. Due to its bland flavor it is used as a carrier and stabilizer of aromas, as well as in some pharmaceutical products. It is also used as a nutrient. Field of view size: 2.97 x 4.45 mm (0.117 x 0.175 in)