The scientific study of hair, scalp, hair care and associated diseases and disorders is called trichology.
It’s important for every hairstylist to be well versed in trichology because healthy hair is essential for any hairstyle and healthy hair starts with a healthy scalp. Stylists must understand elements of trichology like the life cycle of hair growth and the anatomy of the scalp. What’s more, failure to identify an unhealthy scalp condition could actually help sustain a communicable disease or cause hair loss.
This chapter will cover the specifics of hair growth, scalp disorders and treatments and the best way to perform a shampoo and conditioning service.
Each strand of hair consists of two parts--the hair root and the hair shaft. The strand itself is made up of a tough protein called keratin. The root dwells below the surface of the epidermis or outer layer of the skin. The shaft is the visible portion of hair that stems above the epidermis.
The hair follicle anchors each hair into the skin. The hair bulb is located at the base of the follicle.
Within each hair bulb, living cells divide and grow in order to build and support the hair shaft. Also within the bulb, blood vessels exist to nourish the cells and deliver the hormones that control hair growth. This hormone activity varies at various stages of life.
The hair root is composed of the hair follicle, the hair bulb, the arrector pili muscle (also called the hair erector muscle, the dermal papilla and sebaceous glands.
The average scalp measures approximately 120 square inches or 770 centimeters. The average human head contains about 100,000 hair follicles. Each follicle is capable of producing about 20 individual hairs in a person’s lifetime. On average, a person loses or sheds about 100 hairs a day.
The hair follicle is a mammalian skin organ. It’s a tubular shaped shaft that extends from within the skin or scalp and contains the hair root. It extends upward from the dermis, or inner layer of skin, through the epidermis, or outer layer of skin.
It is not unusual for multiple hairs to grow out of one follicle. While hair grows at different rates for different people, the average rate is about one-half inch per month. The hair follicle also contains the pigment cells, which determines the color of the hair. As an individual ages, these pigment cells die, causing the hair to turn gray.
The hair bulb is located at the base of the follicle. It’s characterized by its thick, bulbous shape and it is attached to the dermal papilla. Vascular loops within the hair bulb help to nourish the hair root.
The arrector pili muscle is an involuntary muscle that responds to cold or to emotion. This is the muscle that causes goosebumps, and makes your hair “stand on end” when you’re frightened or excited.
Sebaceous glands are attached to the hair follicle, and they produce a waxy oil called sebum that lubricates and protects the hair and skin. Sebaceous glands are located everywhere on the body, except on the soles of the feet and the palms of the hands. The largest concentration of sebaceous glands is on the face the scalp. Over-production of sebum may cause breakouts, acne or blockage and irritation of the hair follicle. Hair follicle blockage is caused when the sebum becomes waxy and hard, and it can hinder hair growth.
Under-production of sebum can cause hair and skin to feel dry.