Sunday, March 15, 2009

What is Hair and Why is it So Different Among People?

Nora from Altoona, PA, wanted to know more about hair. She wrote in asking several questions about hair including: Is human hair different from animal hair? What is hair made of? Why is hair so different among the people she knows? These are all great questions about hair! So we will first learn some background about hair (e.g., structure, physical properties, and growth patterns), and then we’ll answer the questions.

We generally just think of humans having hair on the head and face but all land mammals have hairy skins. Humans are actually covered all over their bodies with hair except for the palms of the hands, soles of the feet and lips. Even though there is less visible hair on humans compared to other mammals (e.g., cats, dogs, chimpanzees), a square centimeter of human skin actually contains a greater number of follicles (or hair producing sites) than the same sized area of other mammals. The hair all over our bodies is less visible because we have lost the requirement for insulating our bodies, while mammals have not. Hair has more cosmetic value for humans but it also is for protection. For example, hair around the eyes, ears and in the nose prevent dust, insects and other debris from entering those organs where they could cause damage.

A hair is an outgrowth of the epidermis, or outermost part of the skin. Hair consists of the hair follicle and the hair shaft. The hair follicle is the point from which the hair grows, and it is a tiny cup-shaped pit buried deep in the fat of the scalp. The follicle is actually where the pigment, or color, of hair is produced. This pigment is called melanin and is carried upwards into the inner part of the hair as it grows. The hair shaft is the part of the hair that can be seen above the scalp. It consists mainly of dead cells that have turned into keratins (a special protein that is resistant to wear and tear, which is made up of very large molecules) and binding materials with small amounts of water. The center part of the hair shaft is called the cortex, while the outer layer is called the cuticle. If one thinks of the hair shaft like the trunk of a tree, then the cuticle would act as the bark protection the inner cortex where all its moisture lies. If the “bark” of the hair is well cared for, then the whole hair should remain in good condition. However, if the “bark” of the hair is damaged or stripped, then the exposed center of the hair may break.

Now that we know a little more about hair, we can answer Nora’s questions. We learned what hair is made of, but why is hair so different among the people she knows? In general, the type of hair you have is inherited from your parents. It’s actually possible that your hair type might be determined by the part of the world in which your ancestors came from. Nora also asked about animal and human hair differences. The coating of animal hair insulates just like human hair, but it also provides protection from rain. The growth pattern of hair for animals is more synchronized (or growing together), while human hairs tend to grow independently. Humans get their hair cut to their individual desires, while animal hair grows to a certain point and sheds (falls out) at certain times during the year (i.e., shedding often occurs when the coat is too heavy for the weather conditions related to the season) to be replaced by new hair when needed. Human hair is generally the same texture, but animals usually have two textures: there is a coarser top layer of hair and a finer layer (called under fur). These different textures help to insulate the animals. Another feature of hair on mammals is that sometimes their hair color blends with their surroundings, which provides protection against most predators.

Little Lion Experiment
As we have just learned, hair serves the purpose of body insulation and protection from other outside elements for both humans and mammals. This experiment will allow you to determine if the shade of human hair has an effect on its ability to insulate the human body.

You will need: access to dark colored hair and light colored hair (see if you can have the scraps of hair left behind at barber shops or hair salons), a scale (something that can measure in ounces), gloves, an apron or shirt that can get dirty, six paper lunch bags, two thermometers, a heat lamp or constant light source, ruler, stop watch and materials to record your results.

1) Collect the two different colors of hair from a barber shop (you will need approximately 6 ounces in weight of each color);
2) With gloves and apron on, put 1 ounce of each hair color into two different paper bags (remember to keep the hair colors separate);
3) Label the bags according to the type of hair inside and the weight;
4) Close the bags by folding the top down;
5) Repeat Steps 2-4 but put 2 ounces of each hair color into two more different paper bags;
6) Repeat Step 2-4 but put 3 ounces of each hair color into the last two paper bags;
7) Place the thermometers on a table about 15 inches apart from each other;
8) Put the 1 ounce bag of dark hair on one thermometer, and put the 1 ounce bag of light hair on the other thermometer;
9) Place the heat lamp approximately 10 inches in front of the bags and also try to center the lamp (center the lamp so that the light is evenly hitting both bags of hair);
10) Record the temperature changes every two minutes over a total of 10 minutes (do not leave the experiment while in progress);
11) Repeat Steps 8-10 for the other weights of samples;
12) You may want to repeat the experiment more than once for each weight of hair but that is up to you!

Look at your results. How do the temperatures recorded from under the dark hair samples compare to the temperatures under the light hair samples? Hopefully, your experiment was a success and you determined that the dark hair samples showed the greatest temperatures, whereas the bags containing the light hair showed the lowest temperatures. What does this mean exactly? Similar to light and dark colored clothing, dark hair absorbs heat better than light hair. So on sunny days, dark hair will prevent heat from passing through to your head while light hair will allow more heat to pass through.