The hair shaft consists of three main layers: the cuticle, cortex, and medulla. Each of these layers plays an essential role in the structure, strength, and function of the hair, and they are composed of specific proteins and components.
1. Cuticle
• Structure: The cuticle is the outermost layer of the hair shaft, composed of several layers of flattened, overlapping cells (like roof shingles). These cells are dead and contain keratin, a fibrous protein.
• Key Constituents:
• Keratin: A tough, fibrous protein that provides strength and resilience to the hair. It’s the main protein in the cuticle as well as in the cortex.
• Lipids: Fatty substances that help to waterproof the cuticle and reduce friction between the layers, aiding in smoothness and shine.
• Pigments: Though the cuticle itself doesn’t typically contain pigment, it plays a role in the way light interacts with the hair shaft, affecting the appearance of color.
• Function:
• Protection: The cuticle shields the more delicate cortex from external damage such as UV radiation, pollutants, and chemical treatments.
• Moisture Retention: The cuticle helps to prevent the loss of moisture from the hair shaft, maintaining its hydration.
• Shine and Smoothness: When the cuticle is smooth and intact, it reflects light, giving hair its shine and soft texture.
• Thermal Protection: The cuticle acts as a barrier against heat damage from styling tools, but if damaged (e.g., from excessive heat or chemical treatments), it can lead to frizz and breakage.
2. Cortex
• Structure: The cortex is the middle layer of the hair and makes up the majority of the hair shaft’s mass and strength. It is composed of elongated cells filled with keratin and other proteins. The cells are arranged in a spiral or helical pattern.
• Key Constituents:
• Keratin: Like the cuticle, the cortex is primarily made of keratin, which is organized into microfibrils that give the hair its strength and flexibility.
• Melanin: The pigments responsible for skin hair color are located in the cortex. Eumelanin (black hair and brown) and pheomelanin (yellow and red) determine the color and tone of the hair.
• Sulfide Bonds (Disulfide Bonds): These are strong chemical bonds between sulfur-containing amino acids (cysteine) in the keratin molecules. They provide strength and elasticity to the hair. Chemical treatments like perming or straightening break and reform these bonds.
• Water and Lipids: The cortex contains some moisture and lipids that contribute to the elasticity and flexibility of the hair.
• Function:
• Strength: The cortex is the structural core of the hair, providing the strength and elasticity needed to withstand pulling and tension.
• Color: The pigmentation in the cortex determines the natural color of the hair and can be altered by environmental factors or chemical treatments.
• Elasticity: The flexibility of the cortex allows the hair to stretch and return to its original shape, giving it natural movement.
• Heat and Chemical Resistance: While the cortex can be altered by chemical treatments (like bleaching or perming), it remains critical for maintaining the hair’s basic form and texture.
3. Medulla
• Structure: The medulla is the innermost layer of the hair shaft, and it is often absent in finer or thinner hair types. It is a central, hollow core that is composed of loosely packed, irregular cells.
• Key Constituents:
• Keratin: Like the other layers, the medulla is made up of keratin, but it is not as densely packed or structured as the cortex.
• Air: The medulla may contain air pockets in the absence of cells or in cases where it’s less developed. This contributes to the overall lightness of the hair.
• Function:
• Support: While the medulla doesn’t contribute much to the mechanical strength of the hair, it can help provide some structural support, especially in thicker, coarser hair.
• Insulation: The air spaces in the medulla can contribute to thermal insulation, providing some degree of protection from extreme temperature changes.
• Not always present: The medulla is often absent in fine or thin hair. In thicker, coarser hair, it may be more pronounced.
No, polycystine linkages (or more commonly, disulfide bonds) do not reside in the medulla of the hair shaft. Disulfide bonds, which are responsible for linking sulfur atoms between cysteine molecules in the protein keratin, are primarily found in the cortex of the hair.
Here’s a breakdown of where key elements are located in the hair shaft:
• Medulla: The innermost layer of the hair shaft, often made up of loosely packed cells or air pockets, and is absent in finer hair types. It doesn’t contain significant amounts of keratin or disulfide bonds, making it more structural and less involved in hair strength.
• Cortex: This is the thickest part of the hair and contains the keratin fibers that give the hair its strength, elasticity, and color. Disulfide bonds are present in the cortex, linking the sulfur atoms in cysteine amino acids, which helps the hair maintain its structure.
• Cuticle: The outermost layer consists of flattened, overlapping cells that protect the inner layers but does not contain disulfide bonds or polysulfide linkages.
So, to clarify, disulfide bonds are in the cortex, not the medulla, and play a key role in the hair’s strength and shape. The medulla doesn’t contribute significantly to the structural integrity of the hair, especially in finer hair types.
Summary of Functions:
• Cuticle: Protects the inner layers and regulates moisture content.
• Cortex: Provides strength, elasticity, and color.
• Medulla: Offers structural support (less significant in finer hair).
Key Points on Hair Health and Damage:
• Cuticle Damage: External stressors (e.g., heat, chemicals, friction) can damage the cuticle, causing it to lift or break. This results in frizz, dullness, and weakness.
• Cortex Damage: Damage to the cortex, such as from chemical treatments (like bleaching or permanent dyes), can weaken the hair shaft, reducing its strength and elasticity. This can lead to breakage.
• Medulla’s Role: While the medulla doesn’t directly contribute to the strength of the hair shaft, it helps determine the hair’s overall structure and density. Absence of the medulla in fine hair makes these strands lighter but possibly more prone to breakage.
Each layer of the hair shaft contributes to the overall health, appearance, and strength of the hair. Proper care involves maintaining the integrity of all three layers through moisturizing, protecting from heat and chemicals, and avoiding mechanical damage.
Hair weathering, characterized by weaker hair, increased shedding, and dry scalp, can occur when certain hair care practices and product choices disrupt the natural balance and function of both the hair and scalp. Let’s break down how specific methods—like the LOC method, apple cider vinegar (ACV) use, and the application of heavy oils like flaxseed oil—may contribute to these issues, leading to hair weakness, shedding, and a blocked scalp that prevents the natural moisture from reaching the hair.
1. LOC Method (Layering Products)
The LOC method (Liquid, Oil, Cream) involves layering products in a specific order: first, applying a liquid (water or leave-in conditioner), then an oil, and finally a cream or butter. The goal is to seal in moisture and improve hair hydration. However, if not done properly, this method can contribute to hair weathering in the following ways:
• Excessive Product Build-Up: Layering too many heavy products, especially oils and creams, can create a coating on both the hair and scalp. Over time, this build-up can block hair follicles, impair the natural sebum (oil) production, and prevent proper moisture absorption into the hair shaft.
• Follicular Blockage: Oils like coconut, castor, or flaxseed, when not absorbed properly or used excessively, can clog the hair follicles. This leads to an inability for sebum to reach the hair, leaving the scalp feeling dry. This blockage disrupts the scalp’s ability to naturally hydrate the hair, causing dryness, irritation, and possibly even hair thinning or shedding.
• Weakening of Hair Structure: When moisture is sealed in too tightly by oils without proper absorption, the hair shaft may become heavy, causing it to lose its natural bounce and flexibility. This can lead to hair breakage and weakened strands over time.
2. Apple Cider Vinegar (ACV) Use
Apple cider vinegar is often used in hair care for its purported clarifying and pH-balancing effects. While it has some benefits, improper or excessive use can contribute to hair and scalp issues:
• Stripping the Scalp: ACV is acidic, and using it too frequently or in high concentrations can strip the scalp of its natural oils. While this might seem to solve oily scalp problems temporarily, it can also disrupt the scalp’s natural balance, causing overproduction of oils in the long run. Over-stripping the scalp also means the hair may lack the necessary oils to stay moisturized and protected.
Watch full lecture on ACV
• Scalp Irritation and Dryness: ACV can irritate the scalp over time. Sometimes this starts years after one use. This irritation can lead to dryness, flakiness, and even scalp inflammation, making it harder for hair follicles to function optimally and release sebum.
• Disrupting the Acid Mantle: The scalp has an acid mantle (a thin layer of oils and sweat) that helps maintain its natural pH and protect from microbial infections. Excessive ACV use can alter this protective layer, leaving the scalp more vulnerable to dryness, clogged follicles, and potential infection.
3. Heavy Oils Like Flaxseed Oil
Oils like flaxseed oil are often praised for their nourishing and moisturizing properties, particularly for dry or damaged hair. However, using heavy oils without understanding your hair’s needs can contribute to hair weathering:
• Clogging Follicles: Heavy oils can coat the scalp, preventing the natural flow of sebum to the hair and causing follicle blockages. While flaxseed oil contains omega-3 fatty acids that benefit hair health, applying it excessively or not allowing it to properly absorb can contribute to greasy buildup, which clogs pores, impedes sebum production, and leads to hair weakness and shedding.
• Over-Moisturizing: Applying too much oil to the hair or scalp can cause hair to become overly moisturized on the outside but under-moisturized on the inside. This creates a false sense of hydration, and the hair can become limp and prone to breakage. Additionally, excess oil on the scalp can trap dirt and debris, further exacerbating follicle blockage.
4. Blocked Follicles and Scalp Health
The key issue here is the follicular blockage that arises when the scalp is coated with heavy oils, products, or even improperly diluted ACV. This blockage prevents the natural sebum from traveling down the hair shaft, which leads to:
• Dry Scalp (Not Really Dry, But Blocked): The scalp itself may not be dry in terms of a lack of oil production, but the oils are blocked from reaching the hair because of the buildup from product layers or improperly absorbed oils. The scalp may still feel greasy, but the hair may feel dry and brittle because the moisture can’t penetrate the strands.
• Reduced Sebum Flow: Sebum is a natural moisturizer produced by the sebaceous glands. When hair follicles are blocked by product buildup, this natural oil cannot nourish the hair, leading to hair that feels dry and brittle, ultimately resulting in breakage and shedding.
• Hair Follicle Dysfunction: Continuous follicle blockage prevents proper hair growth cycles. When follicles are clogged, hair may shed prematurely, and new growth may be weaker. Over time, this can result in thinning hair and increased shedding.
5. The Cycle of Damage and Weakness
When products like oils, creams, or ACV are layered incorrectly or excessively, the natural moisture balance is disrupted. Hair becomes weak because it is deprived of the sebum it needs for natural lubrication and protection. As the cuticle (the outer layer of the hair) becomes damaged or overloaded with product buildup, it becomes less smooth and more prone to friction and breakage. This leads to a vicious cycle:
• Blocked follicles → Lack of sebum → Hair moisture deficit → Weak hair → Breakage and shedding → Dull appearance → Increased product use → Further follicle blockage.
• The LOC method and heavy oils can result in a greasy, product-coated scalp that blocks natural sebum from moisturizing the hair properly.
• ACV, while beneficial in moderation, can irritate and dry out the scalp if overused, disrupting the natural balance.
• These practices, when done incorrectly or excessively, lead to follicular blockage, preventing the scalp’s natural oils from reaching the hair, which causes dry, brittle hair, increased shedding, and scalp irritation.
To avoid hair weathering:
• Moderation is key—avoid overloading the hair with products and oils.
• Clarify and exfoliate the scalp occasionally (but not with harsh chemicals like ACV too often) to keep follicles free from buildup.
• Allow hair to benefit from natural sebum production, using lighter, more absorbable oils or leave-ins to seal moisture without blocking the scalp.
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