Polarised light micrograph of the root of a human hair. It can be clearly seen how cells that are initially still alive and loosely connected, become heavily condensed over time and lose fluid. Hair that was in the shaft is still embedded in sebum. Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The outer layer (cuticle) of the hair consists of flat, keratinized, dead cells that give the hair its microscopic scaly surface. Inside, the hair consists of cemented keratin fibres (fibrils), which give the hair its elasticity and stability. If melanin is stored, the hair appears black, brown or reddish (two different types of melanin), in very blond people the melanin content is low. Hair serves to protect against heat and cold and also mechanical stress. Magnification: x100 when printed at 15 centimetres wide.