Hair Treatment - Human Hair

 Human Hair

Introduction

Hair first arrived on the evolutionary scene some 310 million years ago on reptilian-like animals, preceded and survived the rise and extinction of the dinosaurs and emerged as the dominant skin appendage of the class of mammals. As members of this class, modern humans have “inherited" skin which, although bearing several million hair follicles covering 95% of the body, have largely confined growing hair to the scalp. 

 

 

Human Scalp Hair

Unlike our primate cousins, we, the fifth and Naked ape, do not possess an all-encompassing, thick, and pigmented pelage. Once the body wide intrauterine lanugo hairs are shed, visible follicular activity is confined to the scalp, with secondary sexual sites a poor second even after puberty.

Since the human head bears some 100,000 – 150,000 hair follicles, an individual adult with 30 months continuous, un-styled growth at 0.9 cm per month will carry some 30 kilometers of hair. This is a significant investment in protein and energy consumption.

Function of Human Hair

The function of human hair is, curiously, unresolved. Hypotheses vary: is it a relic of an aquatic phase of human development where a pelage would be an impairment, or an integral adaptation for thermoregulation and ultraviolet protection? Is it a mere adornment, or the result of FISHERIAN runaway sexual selection? All of these theories can be disproved, not least by the tendency for humans of both sexes to bald. Sociological research has suggested that hair is often interpreted as a marker of age, health, nutrition, and fecundity. In its styled form, it is employed in all societies to express social status or cultural affiliation. Hair in most cultures is at its zenith on the wedding day. By Contrast, sociological studies have reveled the full impact of so-called Bad Hair Days where subjective and objective negative assessment of hair may reduce self-esteem.

 

Modern hair care involving the use of many products is an (almost) ubiquitous human habit in the twenty first century. These products are increasingly deigned to repair and protect hair from environmental and self-inflicted damage while preparing it for styling. 

 

 

Structure of Hair

Many other publications describe in details the human hair follicle, its unparalleled metabolic activities, and its failings. Is the end product of this activity The Human Hair Shaft which we discuss in this chapter.

There are three essential types of hair in humans, which are dependent to some extent on the size of the follicle.

Lanugo Hair

Lanugo hair is fine and non-modulated hair which appears on the fetus, and with rare exceptions is shed prior to or immediately after birth. 

 

Vellus Hair

Vellus hair is fine, short and none or lightly pigmented (less than 40 microns in diameter) and s the most numerous of human hairs. It can be seen from the neonatal period onward covering all surfaces other than the palms of the hand and soles of the feet. At puberty, some vellus hairs enlarge to become terminal hairs, and develop sebaceous glands. Vellus hairs occur on the scalp but are far less numerous than terminal hairs.

In male and female pattern hair loss, terminal hairs miniaturize and return to the size of vellus hairs. This can be reversed with treatment.