Jonathan Adler

Adrienne Antonson

The Biology of Hair - Structure and Function of Hair Follicles

The Biology of Hair

Structure and Function of Hair Follicles

By Heather Brannon, MD

Hair is much more complicated than it appears. It helps transmit sensory information and creates gender identity. Hair is important to the appearance of men and women. There is hair on all the major visible surfaces of the body. It is also the only body structure that is completely renewable without scarring. This article explains what exactly hair is and how it works.

Hair Origin
A developing fetus has all of it's hair follicles formed by week 22. At this time there are 5 million follicles on the body. One million of those are on the head, and 100,000 are on the scalp. This is the largest number of follicles we will ever have - follicles are never added during life. As the size of the body increases as we grow older, the density of the hair follicles on the skin decreases.

Hair Anatomy
Hair has two separate structures - the follicle in the skin and the shaft we see.

Follicle - The follicle is a stocking-like structure that contains several layers with different jobs. At the base of the follicle is a projection formed like sticking a finger in the bottom of a stocking and pushing it in a small amount. This projection is called a papilla and it contains capillaries, or tiny blood vessels, that feed the cells. The living part of the hair is bottom part of the stocking surrounding the papilla called the bulb. This bottom part is the only part fed by the capillaries. The cells in the bulb divide every 23 to 72 hours, faster than any other cells in the body.

The follicle is surrounded by two sheaths - an inner and outer sheath. These sheaths protect and mold the growing hair shaft. The inner sheath follows the hair shaft and ends below the opening of a sebaceous (oil) gland, and sometimes an apocrine (scent) gland. The outer sheath continues all the way up to the gland. A muscle called an erector pili muscle attaches below the gland to a fibrous layer around the outer sheath. When this muscle contracts, it causes the hair to stand up.

The sebaceous gland is important because it produces sebum which is a natural conditioner. More sebum is produced after puberty. The sebum production decreases in women throughout their lives. The production also decreases in men, but not as much as in women
.

Shaft - The hair shaft is made up of dead, hard protein called keratin in three layers. The inner layer is called the medulla and may not be present. The next layer is the cortex and the outer layer is the cuticle. The cortex makes up the majority of the hair shaft. The cuticle is formed by tightly packed scales in an overlapping structure similar to roof shingles. Most hair conditioning products attempt to affect the cuticle. There are pigment cells that are distributed throughout the cortex and medulla giving the hair it's characteristic color.

Hair Growth Cycle
Hair on the scalp grows about .3-.4 mm/day or about 6 inches per year. Unlike other mammals, hair growth and loss is random and not seasonal or cyclic. At any given time, a random number of hairs will be in various stages of growth and shedding. There are three stages of hair growth: catagen, telogen, and anagen.

Catagen - The catagen phase is a transitional stage and 3% of all hairs are in this phase at any time. This phase lasts for about 2-3 weeks. During this time growth stops and the outer root sheath shrinks and attaches to the root of the hair. This is the formation of what is known as a club hair.

Telogen - Telogen is the resting phase and accounts for 10-15% of all hairs. This phase lasts for about 100 days for hairs on the scalp and much longer for hairs on the eyebrow, eyelash, arm and leg. During this phase the hair follicle is completely at rest and the club hair is completely formed. Pulling out a hair in this phase will reveal a solid, hard, dry, white material at the root. About 25-100 telogen hairs are shed normally each day.

Anagen - Anagen is the active phase of the hair. The cells in the root of the hair are dividing rapidly. A new hair is formed and pushes the club hair up the follicle and eventually out. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2-6 years. Some people have difficulty growing their hair beyond a certain length because they have a short active phase of growth. On the other hand, people with very long hair have a long active phase of growth. The hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30-45 days explaining why they are so much shorter than scalp hair.

Hair Shape
The amount of natural curl a hair has is determined by it's cross-sectional shape. Hair that is most similar to a circle is straight and hair that is flattened and elliptical is curly or kinky. The more circular the shaft is, the straighter it is. The more elliptical the shaft is, the curlier or kinkier the hair. The cross-sectional shape also determines the amount of shine the hair has. Straighter hair is shinier because sebum from the sebaceous gland can travel down the hair more easily. The kinkier the hair, the more difficulty the sebum has traveling down the hair, therefore the more dry or dull the hair looks.

War God Kachina, unknown Hopi artist, c. 1930-1945

Hypertrichosis

From Wikipedia, the free encyclopedia

"Werewolf syndrome" redirects here. It is not to be confused with Clinical lycanthropy.

Hypertrichosis (also called Ambras syndrome) is an abnormal amount of hair growth over the body;^[1][2] extensive cases of hypertrichosis have informally been called werewolf syndrome,^[3] because the appearance is similar to the werewolf. The two distinct types of hypertrichosis are generalized hypertrichosis, which occurs over the entire body, and localized hypertrichosis, which is restricted to a certain area.^[1] Hypertrichosis can be either congenital (present at birth) or acquired later in life.^[3][4] The excess growth of hair occurs in areas of the skin with the exception of androgen-dependent hair of the pubic area, face, and axillary regions.^[5]

Several circus sideshow performers in the 19th and early 20th centuries, such as Julia Pastrana, had hypertrichosis.^[6] Many of them worked as freaks and were promoted as having distinct human and animal traits.

Hair Art Hat by Japanese Artist Nagi Noda

http://tommybeautypro.wordpress.com/2013/01/23/hair-art-by-nagi-noda/

Hair structure

The Biology of Hair Groth

The Biology of Hair Growth - Valerie Anne Randall and Natalia V Botchkareva 

The danger of hair

Article 'The danger of hair' by Anneke Smelik:
http://www.annekesmelik.nl/DangerofHair0001.pdf

Hair in bread

Human hair seems to be a source that increases the 'quality' of bread. This 'necessary' source for bread is called Cysteine. Most of this hair is been collected in barbershops in China and sold as Cysteine with the sources of feathers or animal hair.
This film of the 'keuringsdienst van waarde' is a research about this topic. The film is in Dutch with parts in English.
http://keuringsdienstvanwaarde.kro.nl/seizoenen/2014/afleveringen/06-02-2014

Jewelry

Hairball of cat

Timeline family

DNA Test

At the moment I am busy with creating a timeline of my family and I found out that actually there were two (known) bastard children in the family, from both my mothers’ and my fathers’ side. This made me wondering about my origin. In the coming week I will do a DNA test. This DNA test gives an overview of a world map where I can see in which parts of the world has the most in common with my DNA. Actually my brother will do the test because it is easier for the lab to do the test with both X and Y chromosomes. I am sure that my brother is my real brother.

Project plan

I am planning now to open up this project for people to join in and to loose more control over the process and final outcome. At the moment I am thinking about a desk where people can bring their hair and learn how to make a ball out of this. Their hairballs will be integrated directly into the hair installation. This would create a Global Hair Project and could stay a work in progress, so the installation will keep on growing. Also the hairballs with have different colors and structure that will add variation to the installation. 

At the moment I am mostly interested in the notion of hair as a source of DNA.

Map with hairballs

I have made a world map of the locations where I made some of my hairballs. The first one is a flat map of the world, the second one is a globe. After this I thought about a universe with the hairballs connected from the floor and after that with the hairballs connected from the ceiling. With a light that creates shadows on the floor like the sun.

Collecting hair

I have been collecting my hair that fell out for over a year. On every different location I have been I created a new ball of hair. All of them have different sizes. The hairball of the city I live has the biggest size, because I have stayed here most of the time. Some of my hairball collecting locations are: Amsterdam, Delft, Kolkata, New York, Berlin, Istanbul, Athens, Ghent, Venice, Paris, Lisbon and Marrakech.