Hair and hair are a feature of mammals, even smooth-looking species like hippos, elephants, rhinoceros, naked mole rats and even whales or whales are no exception.
Although they have shed most of their body hair to adapt to the environment, they still retain their fur to a certain extent.
Hair, hair is a feature of mammals.
But among mammals, humans are completely separate and have a coat, especially the hair is different when compared to other species because if you don’t cut your hair, your hair can grow very quickly. long, while in other species it stops when it reaches a certain length.
So how long can human hair be if not cut? Perhaps people have thought about this, but it has never been verified by actual action.
But that’s okay, people always like to challenge their limits, even though they can’t keep their hair forever, in the US there is a 50-year-old woman who hasn’t cut her hair for 40 years. In March 2016, her hair was recorded by the Guinness Book of World Records with a length of 16.8 m.
The woman with long hair entered the Guinness World Records.
The growth rate of normal human hair is about 1 cm per month. So, if calculated at this average rate, within 40 years, the average person’s hair is only about 5 meters long, so the growth rate of this woman’s length is still quite strange. .
The growth rate of normal human hair is about 1cm per month.
The hair follicle is the basic unit of hair production, and hair is derived from the growth and differentiation of cells in the hair follicle.
There are about 5 million hair follicles in the human body, including 1 million on the head and 100,000 to 150,000 on the scalp. The hair follicles are located in the skin and are regulated by various hormones and growth factors. And each hair follicle also contains a cluster of hair follicle stem cells , which is a rather complex “small tissue”.
These hair follicle stem cells, like the mother of the cells that surround the hair follicle, can continuously divide to provide a constant source of cells for the growing hair follicle. These new cells can differentiate into hair, sebaceous glands, melanocytes, smooth muscle cells, etc.
Approximately 90%-95% of the hair follicles of the adult scalp are normally healthy during the growth phase.
All hair follicle life cycle can be divided into growth phase (Anagen), decline phase (Catagen) and resting phase (Telogen). Approximately 90%-95% of the hair follicles of the adult scalp are normally healthy during the growth phase, 1% enter the recession phase, and 5%-10% are in the resting period.
As the name suggests, hair follicle cells are most active during the anagen process , and this phase lasts 2-8 years. During this phase, the hair follicle stem cells will divide and differentiate in large numbers, and the hair will grow rapidly and have strong vitality.
After the growth phase, the hair follicles will be in the catagen phase for 2-3 weeks. During this phase, the cells in the hair follicle also stop growing and the hair will no longer grow. In addition, the root of the hair will be pushed from the subcutaneous tissue to the vicinity of the hair follicle stem cells.
Hair follicle cells are most active during anagen.
After that process, the hair follicles enter a resting period of up to 2-3 months. At this point, the connection between the hair and the hair follicle will no longer be tight, it can be said that the hair is “dead” and is in danger of falling out at any time. Furthermore, because melanin production is reduced, we can also see that the hair roots are white.
But for recurring tissues like hair follicles, death also means rebirth. In adult mammals, hair follicles are the only structures that self-replicate.
After a hair follicle completes a growth cycle, it enters the next growth phase under the stimulation of the appropriate signals. After a while, a second hair will grow. The old strand of hair may remain intact or may have fallen out and been replaced with a new strand of hair.
Therefore, hair is most prone to shedding when the hair follicle from the resting phase enters the next growth phase . In fact, as humans, we can lose up to 100 hairs per day. But at the same time, the corresponding 100 hairs begin to enter a new growth cycle.
In an ideal state, a person’s hair count would remain stable at around 100,000 to 50,000 strands.
In fact, from the hair follicle cycle introduced above, it can be seen that the hair length has a period of decline and rest, so basically the hair will also have a certain length, not forever.
In other words, the duration of the hair follicle growth phase determines the length of the hair. The longer the growth period, the longer our hair is capable of growing.
In general, the hair follicles of the human scalp only develop for 2-8 years. As a result, the length that hair can achieve is really limited to a few meters.
Because of the long growth period, our hair is constantly growing and needs to be cut, while the hair on your arms, legs, eyelashes and eyebrows only has an active growth period of about 30 years. up to 45 days.
So those hairs will have a faster cycle of shedding and growing than hair, so their length is also very limited and that’s also why hair in these areas will not continue to grow excessively. if not pruned.
Similarly, the hairs of other mammals have a similar growth cycle, the hair cycle of animals is shorter than that of human hair, so they will fall out before it can grow like human hair.