Distribution and density of the hairs in our body is coded in our genes. This program is activated after birth and hair roots are formed at around 8th-10th week of pregnancy. The hairs that cover the fetus are thin, short, and weak. The growth of hairs is completed in the 22nd week. Number of hairs in a fetus does not change much according to gender. Later on in a person’s life, hairs can become dense or rare, owing to factors such as race, age, gender and hormonal state. There are hair roots covering almost all over our body except for the soles, palms, forehead, the areas under the eyes, on and behind the ears.
A hair is made up of the hair root and the hair shaft on it. A hair root is surrounded with two layers. The duty of these layers is to prevent harm to the hair shaft and let the hair grow in the right direction. A hair root is a multilayered structure where every layer has a different function. The papilla is in the base of the hair root and it basically serves to send nourishment to hair cells. The upper layer of the hair shaft is the hard substance called keratin. The innermost layer, which can be seen as the spinal cord of a hair, does not exist in every hair shaft. The second layer, known as the cortex, constitutes most of the hair shaft. The color of hair is mostly determined by the pigment in this layer. The outermost layer is the upper skin of the hair.
Hairs in different parts of the body have their peculiar forms of and limits to growing. Under the control of hormones, hair roots cause hairs of different properties—such as thickness and color—to form. The hairs in moustache, armpits, between the legs, beard, and on the head grow fast and continually. On the other hand, the hairs on our arms, chest, back, legs and including those in the eyebrows grow very slowly and they know their limits. If the person does not own functional testicles, there may be no hair in certain areas of the body except for the hair on his head.
Most of us are apt to think that certain stories make our hair curl; actually, hair erector muscles are the unsung heroes of those stories. Under every hair in the body, there is an erector muscle that makes it move. These muscles have important functions for the body.
Firstly, it helps the oil glands carry out their function. The oil sacks are located on the surface of a hair. The sizes of these sacks are around 0.2-2 millimeters. Sacks are in the form of clusters. Oil glands are also placed all over the body, accept for the soles and palms. They are the natural “lubricants” for the skin and hairs; they protect the skin from the damage of drying up. Every gland under the skin has a channel. There are alveoli that open to every channel. When the hair muscle is stimulated, the hairs become erect and the connected gland start secreting a substance called sebum. The glands empty their contents to the body of the hair.
Regulating the acidity (pH) level of the skin is among the duties of the hair erector muscle and it produces a protective gel. The oily secretion forms a thin layer of gel; as it serves protecting the skin from heat and cold, it is given an antibacterial effect as well. The natural coating of the skin prevents reproduction of harmful germs. The pH level of the skin is 5-6 and it does not allow bacteria to grow. If this substance is not secreted from the skin, the pH acidity shifts toward alkali, moisture level of the skin increases; the fat layer and then the natural coating is damaged. Thus, germs find a suitable environment to reproduce.
Hair erector muscles are also given a role in adjusting body heat. The hairs in the human body are not related to heat isolation. When the body is exposed to cold environments, the mechanisms that increase body heat are activated. When sympathetic nervous system stimulates hair erector muscles, they contract, hairs bristle, and the body heat is tampered through the reduced heat release. Sometimes, even the invisibly small hairs erect and goose bumps appear on the skin. The purpose is to form a screen for heat. They also allow for perspiration in hot weather and help the body to cool down. In addition, hair erector muscles serve as touching receptors as well. The receptors in hairs easily detect objects on the body surface. Hairs that are activated by touch stimulate the nerve tissue in their base. In a way, they keep a round the clock watch for the body; as tiny and unsung heroes.
They say that perfection is hidden in details, which is also very true for hairs. And perhaps, the secret to appreciation lies in recognizing details, and appreciating their perfection.