FOLLICULAR CYCLE
The follicular cycle is asynchronic in humans, meaning that hairs at different phases of the cycle grow at the same time but with varying proportions depending on the body area.
The hair cycle contains three phases:
ANAGEN (GROWTH PHASE)
CATAGEN (TRANSITION PHASE)
TELOGEN (REST PHASE)
1. Anagen:
it consists of six phases.
Anagen I: cells in the papilla make contact with and stimulate the protuberance causing it to grow deeper.
Anagen II: the secondary germ surrounds the papilla and hair begins to form.
Anagen III: Melanocytes start producing melanin.
Anagen IV: the hair reaches the height of the sebaceous gland.
Anagen V: the hair reaches the follicular ostium.
Anagen VI: hair emerges through the skin’s surface.
The hair in the anagen phase is well rooted. When it is pulled out it causes pain and a pigmented root with part of the internal sheath attached to it can be seen.
Anagen hair is the most sensitive to chemical, physical and hormone stimuli and even to infection or inflammation. These aggressions damage the metabolism of metabolically active cells in the matrix. The hair reacts by prematurely completing the anagen phase, changing to the telogen phase. The hair can also become malformed (dystrophic) or irreversibly degenerated.
The duration of the anagen phase varies according to age, season (increasing in the spring), sex, hormone status and genetics.
2. Catagen:
It is the shortest phase, lasting only a few days. Melanogenesis ceases and cell division is stopped. The hair shaft is released from the dermal papilla, creating a keratinized bulb-shaped structure while part of the follicle is reabsorbed.
3. Telogen:
The hair is loose inside the follicle and will fall at any time.
The hair is bulb-shaped without a sheath surrounding it.
The length of the follicle is from half to one third of what it had in the anagen phase.