Milk contains two primary proteins, casein and whey. When cheese is produced these more liquid components, whey and casein, are separated from the cheese. When eaten or taken in oral supplements, whey protein can have significant antioxidant properties (Source: Journal of Dairy Science, December 2001, pages 2577–2583) as well as anticancer properties (Source: Anticancer Research, November–December 2000, pages 4785–4792) because it generates the production of glutathione in the body, which is a significant antioxidant. Whether or not any of those benefits translate into benefit for skin is unknown. In skin-care products it is most likely a good water-binding agent.