Hair Science P2: The Hair Types

Welcome to Part 2 of our   Hair Science series! Last week we explored the anatomy of the hair, how it grows and the hair cycle. In this installment we’re deep diving into hair types.

Our hair is as unique as we are; everyone’s hair is different based on their genes and ethnicity, but did you know hair also differs based on diameter of the shaft, curliness, strength, colour and density/porosity. Each of these can differ, giving us our unique hair type.

Hair Shape

Last week we learnt that hair is made up of three parts: the inner medulla, central cortex and outer cuticle. Pictures of the hair shaft usually depict a cylindrical shaft, but in actual fact our hair is elliptical in shape - like the orbits of the planets around the sun! 

The degree of ellipses determines the curliness of our hair. And the ellipses of a hair shaft is determined by the particular cell arrangement on the cortex:

ortho-cortical cells are on the outside (convex) of the coil, and para-cortical cells are on the inside (concave) of the coil.

Ratios of ortho- and para- cells define the curl pattern, number of curls per unit length, as well as the curl definition. Hair with a high ratio of ortho- to para- cells is straighter and has more cylindrical shaped shafts, while hair with a higher number of para- to ortho- cells is more curly and has more elliptical shaped shafts.

And that’s why some people have wavy, curly or coily hair and others have straight hair! The degree of curliness has several knock-on effects on the overall hair type: stiffness, moisture, porosity.

Stiffness

Hair stiffness is determined by the diameter of the hair shaft as well as the degree of coiliness.

Moisture

Curly hair types tend to have a lower moisture level than straight hair types, as sebum moves slower down a winding hair shaft than a straight one. This leads to straight hair types typically experiencing more oiliness, while curly hair types are typically drier and require more moisture -  but not too much moisture or it may strip the strands of protein and cause damage.

Porosity

Hair porosity refers to the hair’s ability to absorb and retain moisture. Highly porous hair swells during washing as it takes in water, but since it is a poor moisture retainer, it loses this water and dries quickly. This can lead to protein loss, so if you have very porous hair it may be a good idea to add some  hydrolysed protein into your products. Hair with low porosity means it is hard to absorb moisture, but once moisture is there it is retained well. 

Hair porosity is influenced by the degree of curliness; straight hair tends to be less porous, while wavy, curly or kinky hair tends to be more porous; but of course variations and deviations can occur here. 

There is a famous test to tell porosity where you dunk a few strands of hair in a cup of water. If the strands float, you have low porosity, if they initially float and then sink slowly you have normal porosity hair, and if they sink quickly, you have high porosity hair. Unfortunately this test is not particularly reliable so if you try it don’t read too much into it. But there are other characteristics of hair porosity you can look out for: 

Low porosity hair takes a long time to become fully saturated with water when you wash it, hair tends to dry slowly, and products tend to sit rather than sink in.

High porosity hair looks and feels dry to the touch, it tends to be more frizzy, and it dries very fast.

There are different ways to take care of different hair porosities - we will learn more about this in the next blog.

Hair Types

So far we’ve learned about hair coiliness and porosity, and now this brings us to the next part: hair types.

The Andre Walker (Oprah Winfrey’s hair stylist) system of hair types was developed according to the hair properties we have discussed above.

It goes like this: 

Straight, wavy, curly, and coily/kinky hair is numbered 1, 2, 3, and 4 respectively.

Hair texture from fine to medium to coarse is lettered A, B, and C, respectively.

And then these two categories are combined:

There are some recent additions to this since the ‘90s when it was first developed:

Type 3C produces tighter coils than 3B. The curls of this hair type normally have a lot of texture with a corkscrew-like spiral. The coils can range from tight to loose.

Type 4C has more of a freeing definition, more shrinkage, and tight zig-zag pattern. It is also the most densely packed, coarse and fragile of curly hair types.

Here is a rough idea of how each curl type looks:

The hair typing system isn’t the only way to define your hair’s curls or texture, but it is one tool to help us choose the best products to care for our hair.

Male vs Female Hair

There aren’t any great biological differences between male and female hair. However there are other aspects that may differ between the genders such as hair loss (which is genetic), and differences in hair thickness and texture when it comes to body hair (which is influenced by hormones).

pH of Hair and Scalp

The last major important property of hair, not really related to the particular hair type, but extremely important nonetheless, is pH.

Hair is very sensitive to changes in pH.

Hair is acidic and is naturally negatively charged, so anything alkaline/basic can create friction. This can lead to damage and breakage.

Since water is neutral at around pH 7 (which is more alkaline than the hair, which is acidic at pH 3.67), it can actually increase friction between hair strands, cause frizz and make wet hair difficult to comb. But it goes further: at alkaline pH levels, hair has an increased ability to absorb water and swell, lifting the cuticle cells. Water can penetrate the lifted cuticle cells and temporarily break the hydrogen bonds of the keratin molecules making the hair shaft more prone to damage. To smooth down the cuticle cells and prevent damage, we need to ‘seal the cuticle’.

Cuticle cells lie flat and smooth on the hair strand when they are healthy, but can be disturbed by various factors such as the ones mentioned: high pH, too much water or heat, friction, etc, which causes them to lift, giving the effect of frizzy, unsmooth hair. To smooth the cuticle cells down to a flat position, acidic products in the correct pH range need to be used. Often an acidic hair rinse, or ACV rinse is recommended for smooth, shiny and more manageable hair.

Scalp pH is the same as the skin (it is skin afterall!), at around 4.5 - 5.5, however the hair shaft is even more acidic at about pH 3.67.

So make sure when formulating for the hair, that you take the pH into account! Formulating in pH 3-5 is ideal for hair products.

Shampoos don’t have a standardised pH the way skin products do, however salon products do tend to have a lower pH because this is simply better for the hair. ‘

No tears’ shampoo has a pH of around 7, which is neutral, so as not to sting the eyes. This means though, that the shampoo is more basic than the hair shaft and can therefore actually lead to damage; just something to be aware of.

Whew, that was a lot!

But all of this leads to how we should care for different hair types, so please take time to read and understand.  Straight and wavy hair types may struggle with oiliness, dullness and volume, while curly and kinky types may struggle with dryness, frizz or breakage. 

In addition we need to keep pH and hair porosity in mind when formulating for the hair.

Different hair types need extra special care, and makes formulating for hair types a challenge that we’re taking on in the next blog!

References:

There are many excellent scientific articles that went into the research for this blog. This one sums up hair products nicely:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4387693/