Hair is created in a process that is very similar to that of skin.  In fact, hair comes from epidermal cells, the same type of cell that creates skin.  Hair grows from its base in what is called a hair follicle.  New hair cells are created in the follicle and the hair shaft is pushed outward.  The hair shaft contains "dead" cells since there is no blood supply outside of the hair follicle.  Growth of hair is different that the growth of a tree, which grows "up and out."  Hair simply grows "up," and does not widen.  New hair cells create keratin, a tough and flexible protein.  Keratin gives hair its strength.  Hair (on the head) grows at a rate of about 0.4 inches (10 millimeters) per month. 

What is the purpose of hair?

Hair serves multiple purposes.  Some of these duties are more important for other animals.  Here are some examples of hair duties.

Eyebrows - help keep sweat out of the eyes

Eyelashes - help keep dust out of the eyes

Nose hairs - 1.  help keep dust out of the nose, 2. induce sneezing when stimulated (to help remove particles in the nose)

Head and body hair - helps keep in warmth.  This is more important in other animals such as cats, dogs, squirrels, etc.

Underarm hair - acts as a dry "lubricant" to help prevent skin damage from friction

What give hair its color?

Hair contains two types of melanin, the same protein that gives skin its color.  Hair containing a large amount of eumelanin appears black.  Hair containing a large amount of pheomelanin appears red.  Other hair colors contain a combination of these two pigments.

What makes hair curly or straight?

Different hair types have different cross-sectional shapes.  Some hair is round (like a hot dog) and other hair is more oval (like a toothbrush handle).  Slight differences in growth rates of parts of the hair and imperfections in the hair lead to curling.  Internal chemical bonds between hair proteins hold the hair shape.  These bonds can be temporarily changed (with a curling iron for example) or permanently changed by intentionally damaging the proteins (during a hair "permanent" process).

What are goose bumps?

Goose bumps occur when a small muscle called a pilomotor (or arrector pili) muscle attempts to raise the hair follicle.  The purpose of hair raising is to provide a layer of air between the hair shafts that can help trap heat in cold environments.  This is similar to the effect of a thick down blanket or sleeping bag.  Raised hair follicles may also make an animal appear larger and more threatening to enemies.  These functions are more important in animals with fur.  Humans in the past may have had more body hair, making these functions more important in our ancestors.

Illustration - Retouched. http://www.niams.nih.gov/hi/topics/acne/acne.htm.

Photo by Juan de Vojníkov, 17 October 2007.

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