The Science of Textured Hair: Understanding Hair Shaft Structure and Composition

Hair (Dear)  Diary,

When it comes to textured hair, much attention is given to curl patterns and scalp health. However, to truly understand the unique properties and care requirements of textured hair, we need to dive deep into its microscopic structure. In this professional journal entry, we'll explore the fascinating world of the hair shaft, its structure and its composition. We bring to light how these elements contribute to the individualization of curls.

Anatomy of the Hair Shaft

Let’s begin with what we have in common, each strand of hair is composed of three main parts: the cuticle, the cortex, and the medulla. 

Every person has at least 2 of these layers within each hair strand. As outlined above both home care products and professional care products are necessary for holistic textured hair care. A partnership with a textured hair care provider is vital. Now let’s get more granular on the hair’s structure.

Chemical Composition

Hair is primarily composed of proteins, with keratin being the most abundant. In fact, about 95% of hair is made up of keratin proteins. These proteins are held together by different types of bonds. These bonds include:

 Hydrogen bonds - Hydrogen (H) bonds are temporarily altered by changes in two variables, temperature and water. Heat breaks down the hydrogen bonds and it is restored when it cools. This is why your hair curls with a hot curling tool and why it straightens with a flat iron. The manipulation of the hydrogen bonds changes the form of the hair temporarily.

 To repair or preserve hydrogen bonds, moisturizing is necessary.

Salt bonds - these bonds are altered by changes in pH (potential Hydrogen). If a product applied to the hair is more alkaline or acidic, the salt bonds are broken. Shampoos and Conditioners are usually more acidic to restore the hair’s pH.

 To repair or preserve salt bonds, the pH must be balanced to 5.5 which is the standard level for the hair and skin.

Disulfide bonds- known as the bridges in the hair, create and support the internal structure of the hair, they act as a chain that links between two cysteine amino acids (protein) to create tensile strength.

These bonds can be permanently altered and given a new shape as in the case of chemical treatments, but once they are broken, they cannot be restored.

Lipids also play a crucial role, forming about 3% of the hair's composition. These lipids, primarily in the form of 18-methyleicosanoic acid (18-MEA), are bonded to the surface of the cuticle and contribute to the hair's natural moisture barrier.

Melanin, the pigment that gives hair its color, is also present in varying amounts. Interestingly, the type and distribution of melanin can affect how the hair responds to certain treatments and environmental factors. 

There are two types of melanin; eumelanin (brown and black) and pheomelanin (red, orange yellow) A very interesting fact that I must add here is that different ethnicities have different combinations of these two types of melanin, which is why a hairstylist will say “Your hair is pulling red or its lifting brassy”

Cross-sectional Shape

One of the key differences between straight and textured hair lies in its cross-sectional shape. Straight hair has a more circular cross-section, while textured hair is often more oval or asymmetrical, the “more stretched the oval” is the tighter the curl formation. This irregular shape contributes to the way the hair bends and curls as it grows from the follicle.

The Role of Disulfide Bonds

Disulfide bonds are one of the most important factors in determining curl pattern.  For context sake the disulfide bond is the most powerful naturally occurring bond.. The more disulfide bonds present, and the more irregularly they're arranged, the curlier the hair tends to be. This is why chemical treatments that break and reform these bonds (like perms or relaxers) can dramatically change the curl pattern. 

Tensile Strength and Elasticity

The structure of textured hair gives it some unique properties when it comes to strength and elasticity. Due to its curved shape, textured hair can often stretch more before breaking compared to straight hair. However, this same structure makes it more prone to breakage from mechanical stress (like combing or brushing) because the stress is not evenly distributed along the hair shaft.

The raised cuticle scales in textured hair also contribute to its strength in some ways (by providing more surface area for adjacent strands to "grip" each other) but can make it more prone to damage if not treated gently.

Microscopic Differences Between Curl Types

While all textured hair shares some common characteristics, there are microscopic differences between wavy, curly, and coily hair types:

Wavy Hair: Often has a more open curl pattern with an "S" shape when viewed microscopically. The cuticle scales may be slightly more raised than in straight hair, but less so than in curlier types.

Curly Hair: Shows a tighter "S" pattern or even a "U" shape under the microscope. The cuticle scales are more prominently raised, and the asymmetry in the hair shaft's cross-section becomes more pronounced.

Coily Hair: Exhibits the tightest curl pattern, often appearing as a compressed "S" or “Z” coil shape microscopically. The cuticle scales are the most raised in this hair type, and the cross-sectional asymmetry is usually the most pronounced.