The hair follicle is a complex structure responsible for hair growth. It consists of three layers - the medulla, cortex, and cuticle. Genetics and race influence hair type, including thickness, texture, and color. At the base is the dermal papilla which nourishes new hair growth. Hair grows in cycles of anagen (growth), catagen (transition), and telogen (resting) phases. During anagen, hair grows for 2-6 years until entering catagen and telogen phases. Androgens can cause hair follicles in genetically predisposed individuals to shrink and produce finer hair in the telogen phase, disrupting the hair cycle and potentially leading to hair loss. The hair

1. THE COMPLEXITY OF THE HAIR FOLLICLE Dr AnastasiosVekris, Dr Stella Kaouri DHI Medical Group

2. HAIR STRUCTURE Hair is composed by strong structural protein called keratin Each strand of hair consists of three layers An innermost layer or medulla which is only present in large thick hairs. The middle layer known as the cortex. The cortex provides strength and both the color and the texture of hair. The outermost layer is known as the cuticle. The cuticle is thin and colorless and serves as a protector of the cortex.

3. COMPLEXITY OF HAIR FOLLICLE AND HAIR TYPE Genes and hereditary reasons may predispose a person to a special hair type Race and color are responsible for major differences in the nature of hair follicle and texture of hair (thin or thick, straight or curly, dense or not, black or blond color, variety of ratio of hair/follicle)

5. STRUCTURE OF THE HAIR ROOT At the base of the hair follicle is the dermal papilla feed by the bloodstream which carries nourishment to produce new hair It contains receptors for male hormones and androgens

6. The Hair Growth Cycle Hair follicles grow in repeated cycles One cycle can be broken down into three phases. Anagen - Growth Phase Catagen - Transitional phase Telogen - Resting Phase Each hair passes through the phases independent of the neighboring hairs

8. It can vary from two to six years

9. Hair grows approximately 10-15cm per year

11. Telogen Phase - resting phase It follows the catagen phase and normally lasts about 5-6 weeks Approximately 10-15% of all hair are in this phase at an one time. The hair does not grow but stays attached to the follicle. The dermal papilla stays in a resting phase below

12. Formation of new hair At the end of the Telogen phase the hair follicle re-enters the Anagen phase The dermal papilla and the base of the follicle join together again and a new hair begins to form If the old hair has not already been shed the new hair pushes the old one out and the growth cycle starts all over again.

13. Physiology of Hair Loss in Androgenetic Alopecia In individuals who are genetically predisposed to this type of hair loss: Androgens(DHT)directly affect the hair follicle In scalp hair androgens may cause the hair follicle to get progressively smaller the hair to become finer (telogen phase) Disruption of balance between hair in anagen & telogen phase (>15% telogens)

14. Conclusion The hair follicle, as small as it may be, is the most complicated of the skin adnexa Many of the properties and function of the hair follicle are still largely unknown It requires the outmost attention from the hair specialist, as it is as fragile as unique in each individual

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