Human facial hair

Cross sectional diagram of human hair

I thought it would be interesting to take a look at what it is that we spend so much time and trouble (and with traditional shaving, enjoyment) cutting.

A hair shaft is a dead and quite complex structure made mostly from a protein called keratin, it is manufactured continuously (during the Anagen phase) by a small bulb like structure just under the surface of the skin called the follicle. The shaft has three main components, on the outside is the cuticle which is made of flat thin cells.  Next there is the cortex which is the most important bit which consists of bundles of strands of keratin, these give the hair its strength and they also contain the different forms of melanin that give the hair its colour. In the middle is an unstructured area called the medulla.

There are two different kinds of hair, Vellus hair is fine and is what women and children have on their faces, Terminal hair is caused by the action of androgen hormones starting at male puberty and are thicker, longer and darker, this is what we shave.

There is a huge variation in the diameter of human hairs from 17 to 180 µm (0.00067 to 0.0071 in), a ratio of more than ten to one, no wonder that is so much difference in people’s shaving experience. It also varies enormously in its growth pattern and density, not only from person to person but also in different areas of the same person’s face.

The hair density (hairs per square centimetre) of a beard is about double that of the same person’s scalp and about half of the body’s total number of hairs are on the head, a function of the need to provide more insulation for it. The beard grows very approximately 0.4mm per day, which is about 4 times the speed of fingernail growth. Shaving has no effect whatsoever on the rate of hair growth.

Hair readily absorbs water and as it does so it becomes weaker. When fully waterlogged, which takes several minutes, it loses about 80% of its strength. Which means that if you shave after a shower your blade will last five times longer than if your hair was not waterlogged at all.

Each individual hair has a growth cycle with distinct phases. The Anagen phase is when growth occurs, during the Telogen phase the hair is dormant. Different parts of your body have hairs with different growth cycles, which is why for instance eyebrows are shorter than scalp hairs. Hairs in the human beard also have different cycles lengths depending on where they are, the upper lip behaves differently to the chin which in turn differs from the cheeks. You can see this difference when someone grows a full, untrimmed beard.

All fascinating stuff and during a shaving lifetime you will cut through hairs a huge number of times. Just make sure you are not using a multibladed system razor or a lather generated out of an aerosol and then all that cutting will be far more pleasurable.

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  1. Just found this in an Indian government report!: “His face has about 25,000 whiskers, which are as hard and tough as piece of copper wire of the same thickness, and grow at a rate of five to six inches (125-150mm) per year. An average man will spend in excess of 3,000 hours of his life in the act of shaving.”

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