Every human hair has the structural form of a plant, with root and stem.
The stem is the visible part, just the object of our concerns. The invisible part, below the skin, is a root inserted in a bulb; this bulb is the means of nutrition for the follicle. The hair follicle is the generator of stem cells that make hair grow, and is one of the most dynamic and active organisms in our body. This follicle is fed with sebum, produced by sebaceous glands, located at its sides, which gives the hair elasticity and flexibility.
There are about 100,000 to 150,000 hairs on the human scalp, and each one is composed by 10% of water, lipids, trace elements like iron, zinc, iodine, calcium, manganese and pigments such as melanin, -which is a polymer that gives the hair its color-, and 90% proteins. These proteins are called keratins (Greek κερατίνη, meaning “horn”) and are distributed in 6 or 8 layers like wrapped fibrous layers, spiraling to the left on the inner bark. The outermost of these layers is called the cuticle; it prevents drying, and influences their brightness and color.
The human hair keratin is of the type alpha keratin. It is also found in nails and animal horns. Composed by a large amount of sulfur, this type of keratin is very tough, because its fibrous layers are bound together by ties or sulfur bridges; they do not dissolve in water or saline solutions, and are elastic and resistant to breakage, heat, acidity changes and putrefaction, giving the compound a strong structural strength and long life time. The cuticle surrounds the middle part, the cortex, which holds the melanin, which produces the hair color, and a bone in the center of the hair shaft that is responsible for the hair texture and which provides the nutrients from the bulb.
The hair on the human head grows about one-half inch per month. What should be around 6 inches per year. Or what would also say, a millimeter every two days and eight or nine hours. It grows faster between the adolescence and 30 years of age, and in women more rapidly than in men. And it grows faster in summer than in winter.
Material, processing and technic.
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