THE STRUCTURE OF THE SKIN AND THE PILOSEBACEOUS UNIT
The skin is made up of a set of three tissues, arranged one on top of the other, each with different structural characteristics. The epidermis is the outermost layer and is multi-layered and has no blood or nerves. In the next layer, the germinative layer, there is considerable reproduction of liquid rich, turgid, cells which are pushed upwards by new cells and flattened, thereby losing their nucleus, keratinizing and dying off. Excessive keratinization and detachment of these cells causes the skin to flake, forming dandruff. The dermis is a connective tissue underlying the epidermis, mainly characterized by elastin fibres, collagen, blood and lymph vessels. Several skin appendages pass through the dermis, such as sweat glands, hair follicles and sebaceous glands. The dermis also hosts the living part of the hair which is the hair bulb within the pilosebaceous follicle. The hypodermis is the third and deepest layer of the skin in contact with subcutaneous fat and muscle tissue and consisting of connective tissue rich in adipocytes.