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Anatomy of the Hair

When people think of hair, they often think of hair styles or hair care products. People rarely think of the anatomy of the hair. However, hair anatomy, as well as genetics, plays a large role in how our hair looks. By learning about the anatomy of the hair, we can better understand how to care for our hair.

Hair Anatomy

When talking about hair, people are most often talking about the visible strands of hair that grow from their scalps. However, the hair strands are just one part of hair anatomy. Hair is comprised on two elements: the follicle and the shaft.

The Hair Follicle: The hair follicle is a small tube-like opening in the outer layer of the skin. It is where the hair shaft develops.

At the very base of each hair follicle is the dermal papilla, which contains blood vessels that provide the hair with the nutrients it needs to grow. The papilla also contains nerves, which allow us to feel when our hair is being tugged or pulled.

The actual living part of the hair is located in the area surrounding the papilla called the bulb. The cells in the bulb divide faster than any other cells in the body.

A sebaceous gland is also attached to the hair follicle. This gland produces an oily substance called sebum that helps moisturize and protect the hair shaft.
The Hair Shaft: The hair shaft is comprised of dead, hardened protein called keratin. This is the same element that makes our fingernails and the outer layers of our skin.

The hair shaft is divided into three layers, listed from innermost to outermost:
- The Medulla, the innermost layer, which is present only in thick hairs
- The Cortex, the middle layer that provides strength, color and texture to the hair
- The Cuticle, which is thin and colorless and which serves to protect the cortex.
The cortex makes up the majority of the hair shaft.

The Genetics of Hair

While the basic anatomy of all hair is the same, not all hair looks the same. The way your hair looks is determined by your genetics. Therefore, if your mom and dad have curly hair, you're likely to have curly hair as well. Likewise, a child with parents who have straight hair will likely have similar hair. Genetics also determine hair color.

Whether or not a hair will curl is determined by its cross-sectional shape. Hair that looks most like a circle when it is cut in half will be straight. If you have curly or kinky hair, however, your hair is likely to look flattened or be elliptical in shape.

The cross-sectional view of the hair will also help determine whether your hair looks shiny or dull. Straight hair looks shiner than other types of hair because the sebum produced by the sebaceous gland can easily travel down the hair shaft. Sebum has a harder time getting from the base of hair to the tip of the hair on people with curly hair. As a result, curly hair tends to look dry.

Resources

Brannon, Heather (n.d.). The Biology of Hair. Retrieved November 6, 2007, from the About.com Web site: http://dermatology.about.com/cs/hairanatomy/a/

hairbiology.htm.

follicle.com (2007). Hair Structure and Hair Life Cycle. Retrieved November 6, 2007, from the follicle.com Web site: http://www.follicle.com/hair-structure-life-cycle.html.

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