A single strand of hair is made up of three non-living layers, the medulla (the center of the hair shaft) which is surrounded by the cortex (the bulk of the hair strand), and the cuticle which is the outermost layer. The medulla and cortex are wrapped in the protective cuticle layer, whose structure looks like overlapping shingles on a roof.
Follicles, which lie underneath the skin's surface, are the only part of your hair that is the living tissue that actively produces hair. This is where cobalamin, or vitamin B12 and iron assist your red blood cells in carrying oxygen to the hair follicles to help grow and build hair.
This means that the hair strands that you see above the surface of the skin, the medulla, cortex, and cuticle, are dead cells that cannot heal or repair themselves.
The Role of the Medulla
We don’t know much about the medulla as this study from the NIH shows, except that it is a very fragile, non-living material that is absent in some hair types such as extremely fine hair or blonde hair. The medulla may also be involved in split ends and breakage since it provides an area of weakness along the axis of the hair fiber.
The Cortex Determines Hair Structure and Color
The middle and thickest layer of the hair strand is called the cortex. Its strength comes from a material called keratin that is arranged in rodlike bundles that add additional structure with fats and lipids.
The cortex also has a role in determining the strength and shape of hair.
- People with straight hair have cortex shafts that are round.
- Those with wavy hair have oval shaped shafts.
- Individuals with curly hair fibers have cortex shafts that are ribbon shaped.
Fun fact: The pigments in the cortex and medulla help to determine hair color.
Helping the Cuticle Do its Job
The cuticle’s job is to protect the cortex and medulla, but the cuticle is easily damaged by products like shampoo which strips sebum from the hair leaving it exposed to moisture loss and dry and brittle hair. Washing your hair at the proper time intervals protects important natural oils and sebum.
When the cuticle becomes damaged, the fibers of the cortex fray like the strands of a rope and they can split. Leaving split ends untreated can lead to further breakage, because the fraying can move up the hair shaft. Since the cuticle and cortex are dead and can't heal themselves, the only way to get rid of split ends is to cut them off.
When cuticles become damaged from brushing, chemicals, wind, or heat, the proteins, or keratins, of the cortex have a difficult time lying together in a smooth line. So, treating hair gently when brushing, combing, or towel drying will help keep the cuticle laying flat and reduce damage or breakage.
If you style your hair with a hair dryer or flat iron, use a leave-in product with silicone to help protect the hair strands from fraying. You can also help shield your cuticles by styling your hair with heatless, overnight curls. And if your hair is prone to breakage, use hair tools that reduce friction and ripping like choosing silk scrunchies over cotton and spiral hair ties in place of elastic ones.
While they are not living cells that can be repaired, the three parts of the hair strand: the cuticle, cortex, and medulla can benefit from your mindful use of products, and by avoiding friction-causing styling that leaves hair frayed, and damaged.
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