Do you ever wonder why the 1 curly hair has and the other does not? In this blog we tell you exactly how this works! Before we go into this, it is useful to first know where hair actually is and how it is constructed. 

human hair

hair follicles

Hair is tissue that grows out hair follicles† All these hair follicles are spread over our scalp. And did you know that a large part of these hair follicles were already there when you were born?

The hair follicles are not visible, because they are under your skin. Hair follicles have a tunnel/cone-like shape. 

The hair follicles are covered by two sheaths. there is the inner sheath which ends just below the opening of the oil glands and a outer sheath that grows all the way to the oil glands. You cannot see the hair follicles and sheaths because they are under the scalp.

Overzicht foto van haargroei

hair shaft

Which part you can see we is the hair shaft† These are your hair strands that you can see, brush and style. 

The hair shaft is made up of protein that Keratin hot. Keratin is the same protein that, for example, your finger and nail are made up of. 

Each hair shaft grows from an individual hair follicle. The hair shaft is made up of 3 layers: The cuticles, cortex and the medulla.

Functions of the hair follicle and hair shaft

Hair follicles (or in English: Hair follicles): 

Hair follicles determine what hair type you have, for example 1A (straight hair) or for example 4A (coily hair type). It basically determines whether you have curly hair wavy hair or straight hair. 

The type of hair you get depends on the type of hair follicles you have. Are the hair follicles oval shaped? Then you will probably have curly hair. Are they round? Then it means that you have straight hair.

Did you have curly hair when you were little? and now that you're older no more? Then the shape of the hair follicles may have changed. This does not happen to everyone, but it is possible.


oil glands

The oil glands are basically a natural conditioner. They secrete oil and sebum. The oil glands determine whether you have more oily hair or drier hair. 

Is there a high production of oil and sebum? Then you probably have an oily hair type and vice versa. The production of oil and sebum will decrease as you get older. 

An important note with oily hair is that the more often you wash it with a strong cleanser (because you probably want to get rid of the greasy feeling) the more sebum and oil is produced and your complaints may increase. In this case, it might be useful to wash your hair a little less often. 

hair shaft

The hair shaft is therefore the hair that you actually see. It grows from an individual hair follicle (for each hair, you have 1 hair follicle). 

When the hair comes up in the hair follicle, there will be a total of 6 layers. There are then 3 inner layers and 3 outer layers. The outer layers take care of the shape of the hair follicles and the 3 inner layers become the actual hair. The 3 inner layers are the: cuticle, cortex and medulla. 


The cuticle protects the inner layers of the hair. It gives your hair shine and determines your hair quality. The cuticle also ensures that your hair retains moisture and balances the hydration of your hair. 

Do you continuously use heat tools or chemical treatments for your hair? Then the balance can be disturbed and your hair will become dry and brittle. 


The cortex determines the texture and color of your hair. It therefore determines whether your hair is thick or thin. The cuticle protects the cortex. So the healthier the cortex, the healthier your hair will be. 


The medulla is not in every type of hair. The medulla is often found in thick hair. It determines the strength of your hair. 


As stated before, your hair is made up of protein. They are fused together in the hair follicle and harden as soon as they come out of a hair follicle. This protein is also known as keratin. 

Keratin is a very strong protein and is used against many things: combing, styling, heat tools, etc. Keratin is maintained by 2 types of bonds. The Hydrogen in Disulphide.

Disulphide Bonds
The Disulphide bonds are the strongest. Do you do a perm in your hair? then the disulphide bond will 'break' and it will change the structure. This is the reason that your hair can change after you have put on a perm, for example. 
Hydrogen Bonds

Hydrogen bonds are less strong than the disulphide. Hydrogen bonds give your hair flexibility and make it easy to style your hair. 

So as you can read, there is so much more behind our hair than what we can see! Now you know what hair is and what it consists of. But how does our hair actually grow?

How does our hair grow?

The hair growth phase consists of 4 phases. 

  1. Anagen Phase
  2. Catagen Phase
  3. Telogen Phase
  4. Exogenous Phase

Fasen van haargroei

Anagen Phase
This phase represents the growth phase. During this phase, your hair grows 2.54 centimeters per month. The growth phase lasts about 3-5 years. 
Catagen Phase
After the anagen phase comes the catagen phase. This phase lasts about 10 days and is also called a transition phase. Your hair goes into a period of rest and stops growing for several months. 
Telogen Phase
The Telogen phase is a phase in which your hair takes a rest period of about 3 months and therefore stops growing. Your hair will continue to grow in the follicle but stop active growth after a period of about 3 months. 
Exogenous phase
The hair follicles ensure that your hair can actually come out of the hair follicle in the exogenous phase, these hair strands will then fall out. You don't have to worry, because every hair follicle has its unique growth phase. Not all your hair is in the same growth phase, or in the shedding phase. Hair loss is a natural process associated with the growth phase of your hair. As long as your hair grows naturally and the phases are not disrupted, your hair will always grow naturally and you will not suffer from hair loss. 


Your hair follicles determine whether or not your hair is curly. Are they very oval? Then you probably have more spiral curls. Do you have more wavy hair? Then your follicle is oval, but not to the extent of someone with an oval hair follicle. 

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