Hair consists of proteins (65% – 95%), lipids (1% – 9%), trace elements, polysaccharides and water.
Hair has two separate structures – the follicle in the skin and the shaft we see.
A hair follicle anchors each hair into the dermis of the skin. The hair bulb forms the base of the hair follicle. The papilla protrudes into the hair bulb and is responsible for instigating and directing hair growth. Living cells divide and grow to build the hair shaft. Blood vessels nourish the cells in the hair bulb, and deliver hormones that modify hair growth and structure at different times of life.
The follicle is surrounded by two sheaths – an inner and outer sheath. These sheaths protect and mold the growing hair shaft.
The sebaceous gland produces sebum which is a natural conditioner. More sebum is produced after puberty. Sebum production decreases throughout a person’s life. (More in women than in men).
The hair shaft is made up of dead, hard protein called keratin. The hair shaft has 3 major layers:
Cuticle: The outermost layer of the hair shaft. It is made of overlapping keratin cells that works as a protective scale. The cuticle is transparent. General hair condition is largely determined by the condition of the cuticle, since it is the layer giving elasticity and resiliency to the hair.
Cortex: The intervening layer of the hair. It is made of moisture and natural pigment cells (melanin) that give colour to the hair. The cortex makes up the majority of the hair shaft. The cortex is protected by the cuticle and consists of rope-like protein fibres. If the cuticle is damaged, the cortex becomes exposed, allowing for moisture loss. When this happens the cortex unravels, causing split ends and damaged hair.
Medulla (means “marrow”): The innermost layer of the hair. It is made of cells that form a shaft through the middle of the hair and make up less than one third of the hair diameter. Different amounts of medulla may be present in the hair (interrupted or fragmentary), and may even be absent.