Hair grows everywhere on the human skin
except on the palms of our hands and the soles of our feet, but many hairs are
so fine they're virtually invisible. Hair is made up of a protein called
keratin that is produced in hair follicles in the outer layer of skin. As follicles produce new hair cells, old cells are being pushed
out through the surface of the skin at the rate of about six inches a year. The
hair you can see is actually a string of dead keratin cells. The average adult
head has about 100,000 to 150,000 hairs and loses up to 100 of them a day;
finding a few stray hairs on your hairbrush is not necessarily cause for alarm.
At any one time, about 90% of the hair on a
person's scalp is growing. Each follicle has its own life cycle that can be
influenced by age, disease, and a wide variety of other factors. This life
cycle is divided into three phases:
- Anagen -- active hair growth that lasts between two to six years.
- Catagen -- transitional hair growth that lasts two to three weeks
- Telogen -- resting phase that lasts about two to three months; at the end
of the resting phase the hair is shed and a new hair replaces it and the
growing cycle starts again.
A FOUR-STEP SCENARIO
1) Growth phase: anagen. The hair is full of life, its growth is constant and regular, and its root fills the hair follicle all the way to the base. Length: from 2 to 7 years, depending on gender and personal characteristics.
2) Recession phase: catagen. The hair is between life and death. Its root climbs towards the epidermis, loses some volume and its activity suddenly stops. The hair therefore stops growing, but stays in place for another 2 to 4 months.
3) Expelling phase: telogen. The hair is dead but it stays on the head until the root of the hair replacing it is strong enough to remove it. Length: 2 to 4 months.
4) Hair Loss: The freshly regrown hair makes it to the scalp’s surface and the old hair falls naturally.
When the hair is healthy, 85 to 90% of it is in the anagen phase, and 15 to 10% in the telegen phase. During a period of intensive hair loss, such as season hair loss, the difference can decrease and 30% of the hair can be in the telegen phase. That condition is called "effluvium telogen".
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