Special Note: This article departs from my normal style, but I have included it here because the subject of hair styles and hair types is popular. Blonde jokes have done their share to contribute to the general interest in hair types. This article focuses on some of the interesting scientific facts about hair.
"A blonde was cruising down the highway at breakneck speed when a cop pulled her over.
'May I see your license and registration, please?' asked the cop.
Miffed, the blonde said, 'I wish you guys would get your act together. Just yesterday you took away my license. Now today you want me to show it to you!'" ~blondejokes.com
What makes blonde people blonde or curly-haired people curly-haired? Genetics would likely be your answer. So then, what makes blonde
hair blonde or black hair black? And, what exactly is hair composed of and how does it grow? We will attempt to answer all these questions and more in this article on the subject of hair.
You might think it an odd subject to focus on, but the subject of hair has occupied the attention of many people, both male and female, for thousands of years. Early civilizations had dress styles and hair styles which might seem outlandish to us today, but were quite popular back then. Ancient Egyptians preferred to be bald, ancient Greek men commonly wore beards, and some of the Mohawk Indians shaved the sides of their heads. Today, people style and dye their hair in a way similar to how their ancestors did long ago. People with curly hair, during different periods, have straightened it and, at other times, people with straight hair have curled it.
So, what makes straight hair straight and curly hair curly? The type of hair one has depends on the shape of the cross-section of their hair shafts. Imagine that a hair shaft is the size of a telephone pole. Say that we have a straight hair shaft. When we chop it in half and look at the cross section, we see a circle. When we chop a wavy hair shaft in half, the cross section is oval-shaped. Looking again at our enlarged hair shaft, we notice that it appears black and shiny in the sunlight. When we bring it into the shade, it no longer has a sheen. Why is this and what gives hair its color?
Hair color is based on a couple factors: the type of pigment and the amount of the pigment present. There are two types of hair pigment: eumelanin and pheomelanin (2). Believe it or not, black hair and blonde hair both have the same kind of pigment. The amount of eumelanin present determines the degree of shade for people with black, brown, or blonde hair. More eumelanin means darker hair and less eumelanin means lighter hair (2). Red hair gets its own special pigment: pheomelanin (2).
Eumelanin and pheomelanin are contained in the cortex of a hair shaft--of course, both are not present at the same time. The cortex is one of three layers in a hair shaft and it forms the thick, middle layer. In the interior of the cortex is a layer called the medulla. This layer reflects light in different ways, depending on the degree of brightness (2). In the sunlight, the medulla makes hair appear different than in the shade (2). Some black hair tends to have a sheen in the sunlight, while loosing the sheen in lower levels of light intensity. Forming a colorless, thin, translucent coating around the cortex is the cuticle. The cuticle, which encases the entire hair shaft, acts as a protective barrier between the cortex and the dangerous world beyond.
The lower part of the hair shaft, which descends into the skin, is incased in a sock-like structure called the follicle (2). Within the protective enclosure of the follicle, at the bottom end of the hair shaft is a tissue called the bulb (1). Passing in through the bottom of the follicle and into the bulb is a structure called the papilla (1). Tiny blood vessels bring nutrients to the papilla, and, from the papilla, these nutrients find their way into the bulb where they are used to build the cells that form the hair shaft. As the hair shaft grows, it shoves out an older hair shaft, causing natural hair loss and subsequent replacement.
Hair growth is a complex process that involves the division of cells, the supply of nutrients, and the displacement of older hair shafts. It can be simplified into three phases. The first phase is called the anagen phase. Growth cells in the papilla divide rapidly and stack together to from a hair shaft that slowly grows at a rate of about half a foot per year (3). This phase can last up to six years (3). The catagen phase is the next step in hair growth and lasts for two to three weeks (3). At this point, the sock-like hair follicle degrades, shrinking to a sixth of its normal length, but the hair remains in place (2). The papilla (or dermal papilla) separates from the bulb. Now, the blood supply is gone and the hair enters the next phase: the telogen phase. During the telogen phase, the hair sits dormant and ceases to grow. Roughly 10 to 15 percent of all hairs are in this phase at any given time (2). After a couple weeks have passed, the papilla is active again and a new hair shaft begins to grow. As the new shaft moves upward, the old shaft is displaced and the cycle begins all over again. This process may sound simple, but it is very complex. If one part of the mechanism for hair maintenance and growth were not present, such as the proper nutrients, hair would not grow. Imagine life without it.
In conclusion, we have looked at the different colors of hair and types of hair and why they are different. We have explored the structure of hair and what it is composed of, looking at some of its main components. Finally, we have looked at what phases are involved in the complicated process of hair growth and how old hair is replaced. Being aware of such detailed and intricate processes for the growth and maintenance of something that we take for granted causes one to look at hair in a new way.
Works Cited
(1) Brannon, Heather. "Hair Follicle." dermatology.about.com. About.com, 9 Sep. 2007. Web. 26 Jan. 2012.
(2) "How Does Hair Grow?" hairlosshelp.com. hairlosshelp.com, n.d. Web. 26 Jan. 2012.
(3) "Understanding Hair Loss -- the Basics." WebMD. WebMD, LLC, n.d. Web. 26 Jan. 2012.
