Sebum
An oily, waxy substance produced by the sebaceous glands. It moisturises and creates and occlusive film on the skin, preventing moisture loss.
Stratum corneum
The outer most layer of the skin often referred to as the 'horny' layer.
Skin types
Skin types can be classified into four categories - normal, dry, oily and combination. They are determined by the functionality of the oil glands. These are generally inherited traits but can also be influenced by environmental attributes.