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Curls 101: the science & numbers behind curls

Leestijd: 4 minuten

Do you – just like us – sometimes wonder what a curl is exactly, how a curl is created and why some have curly hair and others not? Fortunately, a lot of research has been done on this and we can tell you more about it.

The big curls search

Many great studies have been done on the how, what and why of curls. For this blog we take the literature study “The what, why and how of curly hair: a review” by The Royal Society as a starting point. This research goes in depth and brings together biological, anthropological and chemical factors that play a role in the degree to which hair curls. The research is based on other underlying studies. The Royal Society’s literature study addresses three questions:

  1. What is the structure of curly hair?
  2. Why do some hair fibers curl?
  3. How do curly hair fibers behave?

We will dive deeper into these questions and answers here, which we try to explain as clearly as possible. In this blog, we will not elaborate on the distinction African, Asian or European hair. In many underlying studies, this distinction is the starting point for determining the distinction between different hair and curl types based on ethnicity. Would you like to know more about this? Then read the full study from The Royal Society.

WHAT is the structure of curly hair?

Each individual hair has a growing portion, which is below the scalp, and a dead portion, which is above the scalp. Curly hair is created in the growing part of the hair. That growing part has a number of components. One of those components is the hair follicle. The hair fiber or also called the hair shaft grows from it. A curl or straight hair starts in the hair follicle and is determined by the shape and position of the hair follicle and by the angle from which the hair grows out of your skull.

First of all, the shape and position of the hair follicle determines how curly your hair is. For your understanding: the hair follicle is the growing, living part and the hair fiber the dead part. Curly hair fibers originate in curved or oval hair follicles. Non-curly hair fibers, on the other hand, arise from round hair follicles that are straight and in line with the hair. The more oval and asymmetrical the hair follicle is, the more the hair curls. If the hair follicle is rounder and more symmetrical, your hair is likely to be straight.

Second, the angle at which the hair grows out of your skull determines how curly your hair is. According to the research, the hair is straight (er) when that angle is square, so it grows out of your scalp at a 90-degree angle. If that angle is smaller or larger, which is of course just how you look at it, then chances are that curly hair will grow out of your head.

WHY does one hair not curl and the other hair does?

The ‘why’ of a curl is of course closely related to the ‘what’ of a curl. To find out why one hair curls and the other does not, the research measured anthropological (environment, climate and evolution), medicinal (the status of your health or the effect of medicines on the structure of your hair), biological (genes) and chemical (permanent treatment) factors.

All of these factors can explain the ‘why’ of the curl. Although more and more is known about this through various studies, the code of the curl has not yet been cracked. What we can say with certainty is that your genes, so biological factors, play a major role in the question of why one person has curly hair and another does not: your genes determine that for 85 to 95%. Is one of your parents blessed with a bunch of curls? Then it is more likely that you will inherit curly hair.

HOW does curly hair behave?

The research tried to find out how curls react to certain conditions. You have physical conditions such as stiffness and elasticity, the degree to which your hair absorbs moisture (your porosity), external conditions such as shine versus dullness and smoothness. Furthermore, growth conditions (how fast curly hair grows) were examined.

The study concludes that the underlying studies often rely on ethnic backgrounds for an answer to this question, without considering different curl types. This leads to confusing and meaningless conclusions, so additional studies are needed to answer this question properly.

Facts and tidbits

Also, L’Oréal has ventured into a study on curly hair. Where L’Oréal started its research on the basis of the three conventional ethnic groups (African, Asian and European), L’Oréal eventually developed eight new categories to indicate the degree of straight or curly hair. These categories range from very straight (class 1) to very curly (class 8). L’Oréal answers the question in which category your hair falls on the basis of four factors: the diameter of the wave, curl index, number of waves, how often the curl turns. Some figures:

  • 80% of the world’s population has black to light brown hair.
  • 50% of the world’s population has dark to very dark brown hair.
  • curly hair is more fragile than non-curly hair.

Texture Trends has researched the spending habits of women with curly hair compared to other women. The answer? Curlies spend 100% more on hair products and, on the other hand, spend less money on hairdressers. They prefer to keep that under control by using a variety of products. 60% of the curlies embrace their natural curl (instead of, for example, straightening or blow drying).

Hopefully you now know a lot more about curls! Do you have any questions? Feel free to ask them via Instagram.