How does water change the properties of Lactose?

Spray-dried a-lactose monohydrate is a matrix of amorphous lactose in which lactose monohydrate crystals are embedded. Humidity has no influence on the crystal but amorphous lactose is very hygroscopic: in presence of humidity, it will transform into the crystalline form. This has consequences on the tableting properties of the substance. Thermal Analysis gives you first Information about the water content of your lactose and the consequences for its compressing properties.