Hair, a seemingly simple strand, is a complex biological structure with multiple layers, each contributing to its overall properties. Beyond its visible appearance, hair possesses an intricate internal architecture designed for specific functions. Understanding these deeper components reveals how hair maintains its resilience and unique characteristics.
Anatomy of the Hair Cortex
The hair shaft is composed of three main layers: the outermost cuticle, the central cortex, and sometimes an innermost medulla. The cortex is the primary structural component of the hair shaft, situated between the protective cuticle and the medulla, when present. This layer constitutes the bulk of the hair’s mass, accounting for approximately 80-90% of its total structure.
The cortex is primarily made of keratin proteins, which are fibrous and provide the hair with its strength and flexibility. These keratin proteins are organized into a hierarchical structure. Individual keratin chains form helical shapes and then assemble into intermediate filaments. These intermediate filaments then bundle together to form larger structures called microfibrils, which are further organized into macrofibrils. These macrofibrils are tightly packed within the cortical cells, creating a dense interior for the hair fiber.
Key Functions of the Cortex
The cortex plays a multifaceted role in determining the hair’s physical and aesthetic qualities. Its well-organized keratin structure is important for the hair’s strength and elasticity. The tightly packed keratin fibers, along with chemical cross-links such as disulfide bonds, enable hair to withstand tension and stretch without breaking. These disulfide bonds contribute to the hair’s stability and shape.
Beyond its structural contributions, the cortex is also responsible for natural hair color. This is due to the presence of melanin pigments, produced by specialized cells called melanocytes and transferred into the cortical cells. There are two main types of melanin: eumelanin, which provides brown and black tones, and pheomelanin, which contributes to yellow and red hues. The specific type, amount, and distribution of these melanin granules within the cortex determine human hair colors.
The cortex also influences hair shape, whether it is straight, wavy, or curly. The distribution of disulfide bonds and the hair follicle’s shape contribute to the hair’s texture. For instance, hair with a more oval-shaped follicle and a greater number of asymmetrically distributed disulfide bonds tends to be curlier, while rounder follicles typically produce straighter hair.
Maintaining Cortex Health
Protecting the cortex from damage is important for maintaining hair health and appearance. The cortex, while robust, can be compromised by external factors. Heat styling tools, such as flat irons and curling irons, can cause thermal damage by denaturing keratin proteins and creating pores within the cortex. This damage can lead to dryness, brittleness, and increased susceptibility to breakage.
Chemical treatments, including coloring, perming, and straightening, also directly impact the cortex. These processes often involve breaking and reforming the disulfide bonds within the keratin structure, which can weaken the hair and increase its porosity. Harsh brushing and excessive manipulation can further contribute to mechanical damage. To help preserve the integrity of the cortex, using heat protectants before styling and opting for lower heat settings can reduce thermal stress. Gentle hair care practices, such as moisturizing and conditioning, support the hair’s internal structure and help maintain its resilience.