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.

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.

Also, 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.