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How the hair protects the skin

The main structures of the hair follicle are the cuticle, the cortex, the medulla, the papilla and the matrix.

The cuticle is the outside, horny layer. It is composed of transparent, overlapping, protective cells. These cells connect with cells of the inner root sheath to stabilise the hair follicle. This layer has no pigment.

The cortex is the middle, or inner, layer, which gives strength and elasticity to the hair. It is made up of a fibrous substance formed by elongated cells. This layer contains pigment.

The medulla is the innermost layer referred to as the marrow of the hair. It is composed of round cells. The medulla may not be present is fine hair.

The papilla and matrix are also very important structures of the hair as the papilla is essential for the growth of hair and the matrix is the lower part of the bulb where mitosis takes place to produce the inner root sheath and the hair also.

Hair serves both as a physical protector for the epidermis and to insulate the skin. In areas where there is not a lot of sweating, the hair helps to hold and prevent the loss of sweat. Each hair follicle has a tiny muscle (the arrector pili) attached to it. This contracts when the body is cold making the hair stand up and causing goose-bumps at the surface of the skin where the hair follicles open. This process slows down the passage of air over the surface of the skin and helps maintain the warmth.

The skin’s sweat glands

Eccrine glands generate sweat in reaction to heat, exercise, fever and stress. There are two to four million eccrine glands distributed over the entire body’s surface; however, there are more found on the palms, soles and forehead. The eccrine glands are not connected to a hair follicle like the apocrine glands; they have a duct and pore through which secretions are brought to the skin’s surface. These glands are more active when the body is doing something physically active. Eccrine sweat does not contribute to body odour.

Apocrine glands produce those body odours that like to camouflage. They are tiny, coiled structures attached to the hair follicles found under the arm, in the genital and perianal areas and around the belly button and nipples. After puberty, they secrete a milky, viscous fluid due to stress, surprise and fear or during intercourse. Although this secretion is odourless when first released, the skin’s surface bacteria rapidly feed on the apocrine fats to produce an unpleasant body odour.

Sweat evaporates off the skin so the body is cooled. This occurs because the nerves are activated to send messages to the sweat glands. Minute muscles around the sweat glands contract so that perspiration is pumped out onto the surface of the skin. Meanwhile, blood rises towards the surface of the skin, where the cooled skin lowers the temperature of the blood and creates a cooling cycle.

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