Hair Growth Cycle
Hair is a threadlike filament that emerges from the epidermis of the skin. Each filament grows in a tiny pocket in the skin called the hair follicle, which penetrates into the dermis. It is also where the root of the hair extends down and widens at its base. Found at the very center of the root is the dermal papilla, which contains the capillaries and nerves that supply the hair and carry the nourishment needed to produce new hair. It is also an important structure because it contains the receptors of androgens that regulate the growth of hair. On the average, hair grows about .3-.4 mm/day or about 6 inches a year.
Hair Structure
Hair is made up of strong structural and twisted
protein fibers called keratin. Keratin is the same protein that makes up the
nails and the outer layer of the skin. Each hair strand is comprised of
three layers, namely, the medulla, cortex and cuticle. The medulla is the
innermost layer of the hair that is only present in large and thick hairs.
The cortex is the middle layer of the hair and provides strength, color and
the texture of the hair. Lastly, the cuticle is a thin and colorless
outermost layer of the hair that protects the cortex.
Three Phases of Hair Growth Cycle
Hair follicles
follow a particular ‘growth and rest’ pattern that randomly takes place and
is not seasonal. These follicles grow over a long period followed by a
relatively shorter period of rest. After the rest, hair begins to shred and
newer hair is produced, thus starting a new growth cycle. The hair growth
cycle involves three phases. These include:
·
Anagen
(Growth Phase)
The anagen phase is the active phase of the hair growth
cycle. In this phase, the hair fiber is actively growing from the hair
follicles and out of the skin or scalp. At the same time, the hair follicle
grows down into the deeper layers of the skin to get the nourishment for the
hair. This phase is responsible for the production of newer hair and
continued lengthening of the hair. This process usually lasts about two to
seven years. The hair grows 1 cm per 28 days and about 90% of the hair
follicles are engaged in this phase. People who have difficulty growing
their hair generally suffer from a shorter anagen phase.
·
Catagen (Intermediate/Transitional Phase)
The catagen phase is the transitional stage wherein the
hair follicles prepare themselves for the resting phase. The hair stops
growing and the outer root sheath shrinks to about 1/6 of the normal length
resulting to the formation of the club hair. About 3% of the hair follicles
are in this phase, which lasts for 2-3 weeks.
·
Telogen (Resting or Shedding Phase)
The telogen is the resting stage of the hair growth
cycle, during which no hair is produced. It may last from seven weeks to
three months and accounts for 10-15% of the hair follicles. During this
phase, the hair does not grow anymore but remains attached to the follicle.
This phase allows the old hair to detach itself from the follicle before it
falls out and be replaced with a newer one as it is pushed out of the
follicle. After this phase, it goes back to the anagen stage for another
hair growth cycle.
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