Every time a discussion about hair comes up, you will notice that the word ‘cuticle’ automatically surfaces . So, without getting sucked deep into the chemistry of things, it’s time to have a closer look at what hair cuticles really are.
What are hair cuticles?
Cuticles consist of flat overlapping cells (scales) that surround the core central fiber of hair. We can compare them to shingles on a roof, pointing downwards towards the tip of the hair fiber. Each cuticle cell is about 0.5 μm thick and about 5μm long. Healthy human hair consists of 5-10 layers of those. They are rich in amino acids, in particular the sulfur rich cystine . In fact studies have suggested that the cuticles alone contain more cystine than the core fiber itself.
A closer look at each hair cuticle
Each cuticle cell contains a thin outer membrane, the epicuticle ( estimated between 50-100 angstroms thick). This layer is in turn covered by strongly bound lipids (mostly the fatty acid 18-methyleicosanoic acid) called the F-layer. The F layer represents the outermost surface of hair.
Beneath the cuticle outer cell membrane are three major layers: the A layer, a resistant layer with a high cystine content (>30%); the exocuticle, sometimes called the B layer, also rich in cystine (~15%); and then the endocuticle, low in cystine content (~3%). The cystine rich layer create keratin-associated proteins which are robust structures.
These are the primary layers within one cuticle cell.
Between each cuticle is the cell membrane complex which is often to referred to as cement because it literally does just that: The cell membrane complex (CMC) is the ‘glue’ that binds the cuticle cells together. If you remember from above, there are about 5-10 layers of cuticles in hair, and each layer is being held to each other by this CMC material.
The CMC region and lower cystine regions such as the endocuticle are easily attacked by chemicals such as chlorine, by shampoos, build-up materials, and even mechanical damage from grooming. They are potentially the weakest points of the cuticle.
When you think of your cuticles stacked onto each other, think of lasagna. Each layer is held in place by the sauce in between.
So there you go, this is an overview of what a cuticle is. Next we will discuss the importance of these cuticles on hair.