the knowledge of hair

Hair is composed mainly of the protein keratin. Keratin assembles into rope-like intermediate filaments. The structure of these filaments provides strength to the hair shaft.

Hair growth begins inside the skin in a hair follicle. The only "living" portion of the hair is found in the follicle. The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead".The base of the root is called the bulb, which contains the cells that produce the hair shaft.Other structures of the hair follicle include the oil producing sebaceous gland which lubricates the hair and the erector pili muscles, which are responsible for causing hairs to stand-up. In humans, with little body hair, the effect results in goose bumps.

Strand of human hair 200x magnification

Each strand of hair is made up of themedulla, cortex, and cuticle.The innermost region, the medulla, is not always present and is an open, unstructured region.The highly structured and organized cortex, or middle layer of the hair, is the primary source of mechanical strength and water uptake. The cortex contains melanin, which colors the fiber based on the number, distribution and types of melanin granules. The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is. Asian hair typically has a round fiber and is quite straight. Oval and irregularly-shaped fibers are generally more wavy or even curly.The cuticle is the outer covering. Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water.

Hair grows everywhere on the external body except for glabrous skin, such as that found on the soles of the hands, feet, and lips. It does not grow on mucus membranes either.

Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases. Each phase has specific characteristics that determine the length of the hair. All three phases occur simultaneously; one strand of hair may be in the anagen phase, while another is in the telogen phase.

The body has different types of hair, including vellus hair and androgenic hair, each with its own type of cellular construction. The different construction gives the hair unique characteristics, serving specific purposes, mainly warmth and protection.