Hair is fundamentally a protein matrix, primarily composed of keratin, organized into three main layers: the outer cuticle, the cortex, and the medulla. Hair destruction refers to the breakdown of this structure, typically beginning with the erosion or lifting of the cuticle layer, exposing the inner cortex. Once the cortex, which provides strength and color, is compromised, the fiber loses its integrity, leading to reduced tensile strength, loss of elasticity, and visible damage.
Chemical Processes That Degrade Hair Structure
Chemical treatments cause the most profound destruction by targeting the internal bonds that hold the keratin protein together. The structural anchors are the disulfide bonds, which are strong chemical cross-links within the hair cortex responsible for the hair’s shape and mechanical strength. Treatments like permanent waving, relaxing, and bleaching necessitate breaking these bonds to alter the hair’s structure.
The process often involves high alkalinity (high pH), which swells and lifts the cuticle scales, allowing chemicals to penetrate the cortex. Bleaching is a strong oxidation process, typically involving hydrogen peroxide, which breaks the disulfide bonds and degrades the melanin pigment inside the hair shaft. This oxidation severely weakens the protein structure, leading to a loss of toughness and elasticity.
Permanent waving and relaxing solutions use reducing agents, such as ammonium thioglycolate, which initially break the disulfide bonds to reshape the hair. A subsequent oxidizing agent is applied to reform the bonds in the new shape. If these processes are not carefully managed, the resultant cuticle erosion and bond cleavage can be extensive, leaving the hair porous, brittle, and highly susceptible to breakage.
Destruction Caused by Excessive Heat
High-temperature styling tools, such as flat irons and curling wands, inflict thermal damage by rapidly heating the water content inside the hair shaft. When the temperature reaches 175°C to 215°C, the water inside the hair fiber vaporizes quickly, creating steam bubbles. This sudden expansion creates pressure that can crack and blister the cuticle layer and the cortex, a condition sometimes called “bubble hair.”
Beyond the physical damage from steam, high heat also causes denaturation of the keratin protein, permanently changing its helical structure. When the temperature exceeds 200°C, the keratin begins to lose its organization, which reduces strength and elasticity. This thermal injury results in hair that is stiff, brittle, and incapable of retaining moisture. Heat damage also leads to the loss of lipids from the hair’s surface, which compromises the barrier and increases vulnerability.
Physical Stress and Mechanical Breakage
Mechanical destruction occurs through external physical forces and repeated friction, leading to cumulative damage. Aggressive manipulation, such as vigorous towel drying or harsh brushing, scrapes and lifts the cuticle scales, fraying the outer layer of the hair fiber. This erosion makes the hair surface rougher, increasing friction between strands and causing the hair to become dull and prone to tangling.
Tight hairstyles, including high ponytails, slicked-back buns, and tight braids, create points of constant tension along the hair shaft and hairline. This continuous pulling stresses the hair fiber, leading to breakage at the mid-shaft or around the edges of the face. Abrasive materials, like certain pillowcases or rough hair accessories, also cause friction damage, weakening the hair until it snaps. Wet hair is especially vulnerable to mechanical stress because its internal bonds are temporarily weakened, making it more pliable and easier to stretch to the breaking point.
Environmental Factors
The environment exposes hair to elements that cause slow, progressive destruction through chemical and physical means. Ultraviolet (UV) radiation from the sun is a significant contributor, causing photo-oxidation of the hair’s protein and color pigments. UV rays generate free radicals that degrade the keratin structure, including the breakdown of internal disulfide bonds, which leads to dryness and brittleness.
Swimming in chlorinated pools introduces a corrosive chemical that strips the hair of its natural oils and can also break down the protein’s disulfide bonds due to its oxidizing properties. This leaves the hair dry, brittle, and susceptible to discoloration. Hard water, which contains high concentrations of minerals like calcium and magnesium, compounds this issue. These minerals deposit on the hair’s surface, creating a dull, heavy film that lifts the cuticle and interferes with moisture absorption, further weakening the fiber.