When it comes to fashion accessories, hair is probably the most versatile and effective. All those expensive necklaces and bracelets and gaudy rings can’t match up to a good hair style, but hair isn’t as simple as you might think. Hair is a complex mammalian material that has different parts with different functions. It just happens to be outside your body and can be cut and styled. Hair is not just a material with a biological function; it becomes a part of our psychological identity. Even those suffering from baldness can make use of hair restoration services and enjoy the stylistic aspects of hair.
Although it might not always be obvious, we are covered in hair. Aside from the bottoms of our feet and the palms of our hands, our entire bodies consist of tiny hairs, making it a much more prevalent matter than we might initially believe.
So what is hair and what does it consist of? Let’s take a closer look at the fine anatomy of hair.
Hair consists of two structures: the follicle, deeply embedded in the skin, and the shaft, which is visible to us. The follicle is the skin organ that produces hair and consists of several layers, each with a different function. The hair follicle is an important component of successful surgical hair replacement procedures, as this can be considered the “root” of the hair which successfully continues to grow after transplantation.
- At the base of the follicle is the papilla, which is made up mainly of connective tissue and capillaries that feed the cells.
- Wrapped around the papilla is the bulb or hair matrix, a collection of epithelial cells and melanocytes, which produce the hair’s pigment. The bulb is the living part of hair, and cell division in the bulb leads to the main structures in hair fiber as well as the inner and outer sheaths. Cells in the bulb divide every 23 to 72 hours, which is faster than any other cell in the body.
- Surrounding the follicle are the inner and outer sheaths. These protect and shape the hair shaft. The inner sheath follows the hair shaft and ends just below the opening of a sebaceous gland, while the outer sheath continues up the gland.
- An arrector pili, which attaches to a fibrous layer around the outer sheath, is a muscle responsible for making your hair stand up when it contracts. For those with little body hair, contraction of the arrector pili muscle causes goosebumps.
- Sebaceous glands are found all over the body. These glands produce an oily, waxy substance called sebum. An overabundance of sebum tends to cause acne, but the substance is necessary for the skin’s lubrication. Sebum is vital to hair as it acts as a natural conditioner.
- The bulge is part of the outer sheath and is located at the insertion point of the arrector pili muscle. The bulge contains several types of stem cells, supplying the hair follicle with new cells. The bulge also takes part in healing the epidermis after a wound.
The hair shaft, as mentioned earlier, is the visible part of the hair. The shaft is composed of keratin, which is a fibrous protein that is a key structural component in our nails and the horns of other mammals. The hair shaft consists of no biochemical activity and is considered dead, which is good because cutting your hair would otherwise be a terrifying, painful experience!
The hair shaft is made up of three layers: the medulla, cortex, and cuticle.
- The medulla is the innermost layer of the shaft but it is not always present.
- The cortex is the middle layer and takes up a majority of the hair shaft. The cortex is highly structured and organized and is the primary source of mechanical strength and water uptake. The cortex also contains melanin, which is responsible for skin pigmentation and, in this case, hair color. The shape of the follicle determines the shape of the cortex. A hair’s curliness is determined by the shape of the hair fiber. Asian hair, for instance, tends to have a round fiber and is thus straight. Oval or irregularly-shaped fibers lead to curly or wavy hair.
- The cuticle is the outer covering for the hair shaft. The cuticle is made up of a formation of tightly packed scales set in an overlapping structure, kind of like roof shingles. This structure slides as the hair swells. The cuticle is also covered with a thin molecular layer of lipids that allows the hair to repel water. Most hair conditioner products target the cuticle.