Hair, a common feature on the human body, is more complex than it appears. Each strand is a sophisticated structure, with specific layers contributing to its characteristics. Beneath the hair’s protective outer layer lies the hair cortex, a key component that determines many of hair’s qualities. Understanding the cortex provides insights into hair health and appearance.
The Core Structure of Hair
The hair cortex forms the bulk of the hair shaft, positioned between the outermost cuticle and, if present, the innermost medulla. This layer contributes significantly to the hair’s mass, accounting for 75% to 90% of its total weight. It is predominantly composed of keratin proteins, which are long, fibrous structures. These proteins form strong disulfide bonds that provide structural integrity.
Within the cortex, melanin granules are also distributed, responsible for hair color. The cells within the cortex are compressed and keratinized, meaning they are hardened and filled with keratin.
How the Cortex Shapes Hair Properties
The arrangement of keratin within the cortex contributes to hair’s mechanical properties, including its strength and elasticity. This internal structure allows hair to stretch without easily breaking. Hair with normal elasticity can stretch up to 50% of its original length and return to its natural state.
The type and distribution of melanin within the cortex determine a person’s natural hair color. Eumelanin is the pigment responsible for black and brown shades, while pheomelanin imparts yellow, blonde, red, and auburn hues. The shape and structure of the cortex, influenced by the hair follicle, also play a role in determining hair texture, such as whether hair is straight, wavy, or curly.
Protecting Your Hair’s Inner Strength
External factors can impact the hair cortex. Chemical treatments like coloring, bleaching, perming, and relaxing can disrupt the protein bonds within the cortex, weakening its structure. These processes can also increase hair porosity, creating microscopic holes and cracks within the cortex. Excessive heat styling from tools like flat irons, curling irons, and blow dryers also poses a threat. High temperatures can denature keratin proteins, causing them to lose their natural structure and leading to brittleness.
When the cortex is compromised, hair health and appearance can suffer. Hair may become dull, dry, and brittle due to moisture loss and altered protein structure. Increased breakage, split ends, and decreased glossiness are also common indicators of a damaged cortex. Protecting the cortex by minimizing exposure to harsh chemicals and extreme heat is important for maintaining hair’s strength, elasticity, and vibrant appearance.