The cuticle is the outermost layer of overlapping flattened cells of the hair. It has taken researchers many years to study and understand hair cuticle structure and how it develops in the follicle.
The essential function of the hair cuticle with its tough inelastic protein content is to protect the inner cortex that provides the elastic properties of hair. The scaly structures of cuticles at the surface of hair are often uplifted and cause light scattering and then affect hair lustre.
This blog sets out to deliver a more in-depth understanding of hair cuticle and how it impacts hair appearance and feel, together with several solutions to repair and strengthen damaged cuticle.
The structure of human hair
Hair is a filamentous biomaterial consisting mainly of proteins, keratin in particular. The structure of human hair is well known: the medulla is a loosely packed, disordered region near the centre of the hair surrounded by the cortex.
The cortex contains the major part of the fibre mass, mainly consisting of keratin proteins and structural lipids. This hard-keratin layer constructs the main body of the hair, giving the hair its strength and determining the hair colour, curl pattern, thickness, and texture.
Lastly, the cortex is then surrounded by the cuticle, a layer of overlapping scales of hardened, keratinized tissue, forming a protective sheath. The hair cuticle is critical as it protects the inner structure from being damaged by external factors.
Hair cuticle structure - A closer look
Together with research over 70 years, the use of cell biology techniques has contributed to the knowledge of hair structure and properties and revealed the major details of the internal structure of cuticle cells.
Cuticle cells are about 0,5 micrometres in thickness and about 45-60 micrometres in length, found at approximately 6-7 micrometres apart.
First, there is the epicuticle. It is the outermost layer of the cuticle, a lipid-protein membrane that is only 10-14 nanometres thick. Studies indicated that this fine layer surrounds the whole surface of individual cuticle cells.
Beneath it is the outstanding structural feature of the three layers. The layer closest to the upper surface of each cuticle cell is the A layer with a high cysteine (a type of amino acid) content and a thickness of 50–100 nanometres.
Then comes the exocuticle with again a high cysteine content and a highly variable thickness ranging from 50 to 300 nanometres.
And lower than that is the endocuticle with a low cysteine content and a thickness also ranging from 50 to 300 nanometres.
Figure 2. Transmission electron microscopy of cross-section of human hair with five overlapping cuticle cells. Each cell has a dense A-layer and a less dense exocuticle beneath. The lower layer is endocuticle.
[Source: Known and Unknown Features of Hair Cuticle Structure: A Brief Review]
Besides, there is also the cell membrane complex (CMC) that glues cuticle cells together. It is composed of a lipid bilayer and creates a selective barrier that allows some substances, such as oxygen and nutrients, to pass through the membrane while preventing other substances, such as ions and large molecules, from passing through.
The importance of hair cuticle
In general, the cuticle helps prevent damage to the hair and maintain its overall health and appearance.
Hair cuticle’s role in maintaining hair hydration
While the water content in the medulla and cortex layers determines the hair moisture level, the cuticle plays a significant role in allowing water to enter and exit the hair shaft. As a result, it influences the hair hydration effort in many ways.
As the outermost layer of the hair, the cuticle is more susceptible to damage, which can cause the cuticle scales to become raised. Then, the hair permeability and porosity increase, leading to dry, brittle, and dehydrated hair.
The effect of the cuticle structure on hair characteristics
An ordered cuticle structure is essential for hair lustre and a natural impression.
The surface structure of the cuticle has a significant effect on the natural appearance. The surface roughness of the cuticle affects hair shine caused by the specular reflection (mirror-like reflection) at the surface. In the case of hair with uplifted cuticles, light reflection scatters when a light source hits its surface. And the corresponding hair appearance shows relatively more diffused and unclear lustre.
The cuticle of hair can affect its appearance in another way because of its inclined structure. Typically, the cuticle layer is scaly and inclined in one direction from the root to the tip of the hair. This produces a natural impression via the double reflections from the front and back surfaces of the fibre. However, these reflections are not visible in highly damaged hair that has lost its cuticle.
How to strengthen the hair cuticle?
The cuticle is a highly organised but delicate structure that is susceptible to damage from various forms of trauma, including physical, chemical or mechanical trauma. In particular, the inclined structure of the cuticle is fragile and difficult to control, especially in the case of hair that has lost its cuticle. This can make it challenging to maintain a natural-looking appearance for the hair.
There are many different solutions for repairing and maintaining the surface conditions of hair fibres. Protein is often used in hair care products to treat damaged hair cuticle to repair and restore its natural structure plus strengthening it.
Meanwhile, one of the solutions for cuticle control is covering the hair surface with chemical materials such as oil and polymers. These can smoothen the hair surface and enhance hair lustre.
Remember to apply a super hydrating shampoo and conditioner to increase moisturisation for your hair. Leave-in conditioners or hair masks may be another option to provide extra nourishment for your hair.
Want to tackle more hair problems? Maybe you want to read more about Common hair issues in wintertime
The information we provide is not intended to mitigate, prevent, treat, cure or diagnose any disease or condition. If you have any concerns about your health, please consult your doctor.
Rogers, G.E. Known and Unknown Features of Hair Cuticle Structure: A Brief Review. Cosmetics 2019, 6, 32. https://doi.org/10.3390/cosmetics6020032
Bontozoglou, C., Zhang, X., Patel, A. et al. In Vivo Human Hair Hydration Measurements by Using Opto-Thermal Radiometry. Int J Thermophys 40, 22 (2019). https://doi.org/10.1007/s10765-018-2477-x
Nagase, S. Hair Structures Affecting Hair Appearance. Cosmetics 2019, 6, 43. https://doi.org/10.3390/cosmetics6030043