What Is Hair?

• Compounds in Hair
• Types of Hair Follicles
• What is the Dermal Papilla?

Whether male or female, we are hairy creatures—except for the palms of our hands and the soles of our feet, we are covered with hair. At any given moment, the average man or woman has between 100,000 to 150,000 hairs on their scalp alone.^(5, 6)

The Hair Shaft and Follicle

The hair we see may appear to be a simple structure, but in fact it is highly complex, especially at the microscopic level below the surface of the scalp. The part of human hair we see is made of multiple layers of cells grouped into three main sections (bound together by a cell membrane complex) that comprise the hair shaft:^(6-8)

Compounds in Hair

Human hair is primarily composed of keratin proteins, which are made of amino acids (of which cystine is one of the most important for hair). As hair grows, proteins are synthesized from amino acids in the hair bulb to form the shaft fiber. As these proteins move up through the follicle, disulfide bonds are formed between them to create the stable hair fiber (incorporating melanin pigments for color).⁽⁸⁾

Lipids, melanin pigments, and trace elements compose a tiny but important 3% of hair’s chemical composition. Each of the three sections of the hair shaft are comprised of a different mix of biochemicals:⁽⁸⁾

Types of Hair Follicles

There are three types of hair follicles:⁵

• Vellus—found on most areas of the body
• Terminal—primarily found on scalp, pubic area (after puberty), beard, and underarm areas
• Sebaceous—contains a gland that produces natural oils called sebum; located in all the areas as terminal hair; also on other facial areas, chest, and back

Follicles naturally occur in groups. Each grouping of follicles, or follicular unit, contains a ratio of approximately seven terminal hairs to each vellus hair.^(6, 9)

What is the Dermal Papilla?

The hair follicle is found below the skin. It holds the hair in place, contains the sebaceous glands, and provides nutrients to the hair during the growing phase via blood vessels located in the dermal papilla beneath the hair follicle. Important to hair growth and loss, the hair follicle contains epidermal growth factor receptors, hormone receptors, and vitamin D receptors. It can also produce its own hormones (including melatonin) and growth factors (e.g., insulin growth factor-1).^{(5, 10, 11)}

Besides blood vessels, the dermal papilla contains:^(6, 8)

• Androgen hormone receptors
• Fibroblasts (cells that produce collagen and other structural proteins)
• Growth factors

All of these factors are important to hair growth. ¹²

In fact, one of the ways minoxidil works is by stimulating increased production of growth factors in dermal papilla cells that stimulate follicle cell proliferation. This prolongs the growth phase of hair.⁽¹³)