Have you ever noticed that, until you cut it, the hair continues to grow, while the hair doesn’t? Yet the structure from which they originate, the hair follicleit’s the same! What is the difference then? Hair and hair follow the same life cycle by passing from the phase of growthto that of Stasi and finally of Quiescence, in which they enter a sort of very short lethargy. What differentiates them is the duration of the growth phase (Anagen)which can last several years for hair, while for hair and hard eyebrow A few weeks to a few months. The mechanisms that regulate the growth phase and the transition from one phase to another are the result of one complex interaction Between genetics, hormonal factors and lifestyle and understanding them could lead to new strategies for disorders such as alopecia or treat baldness.
How hair and hair grow up
Hair of the body and beard, eyebrows and hair are basically the same thing: all of the same structures are born, the hair follicles are made of the same substance (the keratin) and follow the same life cycle. In the life of a hair and a hair we can distinguish four phases: growth, involution, rest and fall.
- Growth or anagen phase: the hair follicle is at the maximum of his activity. The cells inside (the keratinocytes) they divide without stopping And this leads to the lengthening of the hair and hair stem, at an average growth speed of about 1 cm per month;
- Involution or catagen phase: the activity begins to slow down and the hair follicle begins to regress due to the planned death (apoptosis) keratinocytes;
- Rest or Togen phase: At this stage, the cell division stops completely and the hair remains “anchored” to the hair bulb only weakly until it falls naturally or for one weak traction (for example, combing the hair);
- Fell or exogenic phase: represents the moment when Capello falls physiologically.
How much hair and hair grow
The difference between hair, beard, hair and eyebrows lies in the duration of the anagen growth phase. For the hair it can last several years (from 2 up to 6 years, based on genetic factors), while for hair in other parts of the hard body only from two to three months. That’s why the hair continues to grow, while, fortunately, the hair of the arms remain short.
The Catagen phase lasts only from a few days to two weeks. The duration of the teogen is also variable from two to three monthsuntil the follicle enters the Anagen phase again.
What the transition from one phase to the other of growth triggers
Taking into consideration the main phases (i.e. growth and rest), the mechanisms that regulate the transition from one phase to another are still unclear, but we can imagine it as a sort of clock Interior made of molecules and signs that accelerate or inhibit the activity of the follicle. This complex life cycle is finely regulated primarily by several hormoneslike thyroid and steroids (estrogen, testosteronedihydrotestosterone).
Other intrinsic factors also come into play. For example, the growth factor of the fibroblasti 5 seems implicated in the termination of the Anagen phase, because it is expressed by the follicle just before the end of this phase, while the growth factors of the fibroblasti 7 and 2 are essential to have a follicle in health and active.
As if it were not already complicated enough, also external factors such as thediet And it lifestyle (and therefore the level of inflammation of the body), as well as the use of some drugs They can speed up or slow down one of the phases.
A mathematical model to understand how hair and hair grow
A study from 2017 identified in mice Two cellular reporting paths which respectively activate (WNT route) and inhibit (BMP) the growth of the hair. The researchers used a mathematical model to predict how the alternation of these two reports of reporting the growth of hair in different areas of the body of micefinding full response in the direct observation of the guinea pigs.
Thanks to this model, in fact, they managed to outline, based on the activation of one path or the other and the presence of specific receptors on the hair follicles, a sort of map of the skin of the mice, with areas with fast hair growthslow or slow and areas instead refractory to the action of these reporting paths.
Understanding how these various factors interact with each other can be a fundamental help to identify new therapies for pathologies such as alopecia or new treatments for baldness.
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