Balneum bath oil contains soya oil and is used to treat dry skin conditions. It is added to bath water to moisturise dry skin. It works by providing a layer of oil on the surface of the skin to prevent water evaporating from the skin surface. Dry skin results from lack of water in the outer layer of skin cells known as the stratum corneum. When this layer becomes dehydrated it loses its flexibility and becomes cracked, scaly and sometimes itchy. The stratum corneum contains natural water-holding substances that retain water seeping up from the deeper layers of the skin, and water is also normally retained in the stratum corneum by a surface film of natural oil (sebum) and broken-down skin cells, which slow down evaporation of water from the skin surface.