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==Development==
==Development==
[[image: Section of Foetal Cat Skin.jpg|thumb|250px|right|A section of foetal cat skin showing developing hair follicles. Copyright RVC2008]]
Hair germs begin from an aggregation of keratinocytes in the stratum basale of the [[Skin - Anatomy & Physiology#Epidermis|epidermis]]. The initiating factor is the underlying dermal fibroblast cells. The keratinocytes elongate, divide and relocate to the dermis. Dermal fibroblasts then form a dermal papilla beneath the hair germ. This causes stimulation of the basal stem cells to up-regulate their cycle, producing cells that will keratinise and form the hair shaft. Two swellings form on the shaft, one containing stem cells for follicle regeneration, the other becomes a sebaceous gland which will secrete sebum onto the hair shaft.
Hair germs begin from an aggregation of keratinocytes in the stratum basale of the [[Skin - Anatomy & Physiology#Epidermis|epidermis]]. The initiating factor is the underlying dermal fibroblast cells. The keratinocytes elongate, divide and relocate to the dermis. Dermal fibroblasts then form a dermal papilla beneath the hair germ. This causes stimulation of the basal stem cells to up-regulate their cycle, producing cells that will keratinise and form the hair shaft. Two swellings form on the shaft, one containing stem cells for follicle regeneration, the other becomes a sebaceous gland which will secrete sebum onto the hair shaft.