Why do eyebrow hairs stop growing?

by Peri Jones

Have you ever wondered why your eyebrow hair is not covering your whole face? It saves time and money on getting it cut, but why does it not grow as long as the hair on your head?

People have hair all over their body. Its prime purpose is to protect our skin by regulating heat so that if we’re cold, it will act as a warm blanket, but when we’re overheating, it will help cool us down.

But what about eyebrow hair? Our skin is covered in hair, including our head, but why do we have these two strips of hair just above our eyes? Does this region of our face get particularly cold? In a similar way to heat regulation, the eyebrows are actually evolved to help protect our eyes from sweat or other contaminants that could fall into our eyes. So there might be a good reason to keep those untamed ‘brows…

We now know why we have eyebrows, but why is the hair so short? Eyebrows come in all shapes and sizes but rarely do they grow longer than a few millimetres. According to the Guinness World Records, the longest eyebrow hair goes to Zheng Shusen which had a single eyebrow hair measuring in at an astounding 19.1 centimetres. However, he did have to keep it behind his ear to avoid it ending up in his dinner.

Hair goes through three phases: the anagen, catagen and telogen phase. The anagen phase is also known as the growing stage. On everyone’s scalp there are about 5 million little hair pockets called follicles where cells and proteins build the root of the hair. The hair will continue in this phase, and grow for between two to six years at a rate of around 15 centimetres a year. This can vary greatly depending on your genes, hence why some people have longer hair than others and why some people can grow their hair quicker than others. A whopping 85% of our head hair is in this anagen phase.

By Healthwise Staff: http://www.webmd.com/skin-problems-and-treatments/hair-follicle

However, the amount of time that hairs can stay in this phase can vary. This is the major difference between the hair on our head and eyebrows. Our eyebrows will only be in this growing stage for less than a month which means it will only grow to a certain length before it stops and moves to the seconds phase: the catagen phase.

The catagen phase is a short transition stage where the hair detaches itself from the blood supply before moving on to the telogen phase. This third and final stage of the hair’s life cycle is when the hair is completely removed from the blood supply and the follicle is left to rest with the hair remaining dormant. Without any blood supply, the hair can no longer grow, but can stay on the head for months before it is shed.

As eyebrows are still useful in protecting the eyes from any sweat reaching our eyes, having some hair there is still necessary. Having a short anagen phase means that the hair will stop growing before reaching the eyes and only healthy uncontaminated hair is used to protect our vision.

Eyebrow fashion changes year after year, from pencil thin to the fuller au naturel look, but this is clearly a personal preference. As mentioned, your genes play a big role in the rate and amount of hair you have so some people will have fuller and longer eyebrow hairs. But fret not, with the exception of a few rogue hairs, your eyebrows will stay a constant length so there will be no need for any eyebrow clips any time soon.

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Posted in Biology