The number of consumers with damaged hair continues to rise due to external factors; for example, mechanical damage from brushing, hair-straightening irons, etc.; chemical treatments such as hair dyeing and bleaching; and environmental damage from the sun, pollution, etc. Once hair is damaged, repair treatments must intervene on several levels to repair it—from the middle of the cortex to the cuticle. However, film-forming agents such as silicones, which are commonly used, cover the hair with a fine waterproof layer, slowing or even preventing the penetration of actives to repair hair. The present article therefore explores the development of a repair serum based on natural actives and omitting such film-formers.
Understanding the structure of hair and how various forces acting upon it can cause damage is key to developing appropriate hair repair treatments. Thus, it is first important to review some of the basics of hair anatomy. The visible part of the hair shaft, i.e., the capillary stem, consists of three concentric layers. The outermost layer or cuticle comprises 6 to 10 superimposed layers of fusiform cells. These scales cover the entire length of the hair fiber surface like tiles on a roof, with their free edges pointing toward the end of the hair fiber. Hair’s health and appearance depends on each of the 100,000 capillary stems present. If the cuticle is intact, smooth and permeable; if it adequately protects the cortex containing the keratin fibers; and if it is not covered with a greasy substance, its shine and volume will be satisfactory. The central part of the hair fiber, known as the cortex, represents two-thirds of the thickness of the hair fiber. It consists of melanin-pigmented cells and long-chain keratin. These fibers are linked to one another by a mass of sulfur-rich keratin known as the matrix. Finally, the innermost medulla is composed of dead cells that have been emptied of their substance; it is absent from children’s hair or very thin hair.
Strength and elasticity: Hair has two basic properties—strength and elasticity. It is remarkably resistant; a single hair fiber can carry a weight of 100 g without breaking, and can extend by 20–30% when dry and 100% when wet without breaking. This resistance is due to the presence, composition and organization of the cortex protein keratin.
Keratin is composed of long, helicoidal chains of 18 amino acids that are compressed to form a regular, resistant and flexible structure (see Figure 1). High concentrations of the amino acid cysteine are responsible for this unique structure due to the strong chemical bond known as a disulfide bridge, which forms between two cysteines from two different chains. This reticulation of keratin chains is responsible for the mechanical properties of hair fibers and contributes to their cohesion and resistance. Protective layer: As noted, the cuticle is composed of scales and serves as an impermeable and protective layer for hair fibers. These scales are solidly assembled by ceramides, a type of “cement” mostly containing lipids. Ceramides play a crucial role by maintaining the hair structure, ensuring proper cohesion of the scales and preventing damage such as hair breakage, dryness and dullness. When the scales are intact, smooth and correctly assembled, they reflect light and give hair its shine and softness.
While hair fibers are remarkably strong and can resist substantial external assault, they are not invulnerable and over time, their natural physical properties of elasticity, resistance, water content, porosity, etc., are negatively impacted. One immediate sign that hair is damaged is the lack of shine. In addition, hair fibers feel rough to the touch and lack elasticity and suppleness. This is due to capillary fibers becoming porous and the loss of constitutive elements such as proteins1—which increases with sun exposure.2 The hair can become difficult to style, unruly, entangled and brittle. In addition, the ends split and hair no longer reacts to traditional shampoo and conditioner care.
External attacks may come from various sources, including: Erosion: Erosion is the progressive wear of the cuticle and its elimination from the capillary stem. This type of erosion is a natural process that can be sped up by various other forms of wear on hair.
Mechanical stress: Hair may also be damaged by repeated brushing and combing. It has been observed that brushing reduces hair sheen by causing small fissures in the cuticle.3, 4
Knots, twists, back-combing and the use of elastic bands or any other type of friction also weakens the cuticle, and cutting hair with blunt scissors or a razor makes cuticle scales particularly vulnerable.
Heat: The too frequent use of heating appliances on hair or their use at too high temperatures via dryers, straightening irons, etc., will damage the fibers. Excess heat damages the hair by reducing its level of hydration and softening the keratin. Furthermore, minute vapor bubbles are formed in the middle of the softened fiber and the cuticle becomes swollen.
Chemical treatment: Lesions also are caused by chemical upheaval of the hair structure. When hair is colored, the cuticle is lifted to allow the chemical dyes to penetrate the hair cortex. Permanent waves, on the other hand, break the sulfur bonds of the hair and re-assemble them in a different way. In bleached hair, under conditions above 60% relative humidity, the space between the microfibrils is increased;5 in relation, Persaud and Kamath showed that above 65% relative humidity, bleaching impacts fiber torsional properties, reducing the shear modulus.6
Environment: UV light has been shown to degrade keratin in the hair cortex. Dubief reported that six months of sun exposure reduces the intercellular cement between cuticle cells.7, 8 In addition, Reutsch observed thinning of the cuticle after exposure to UV light.9 Furthermore, wind can entangle hair and cause friction between the capillary stems, wearing them down.
The Damage Cycle
When the hair fiber is thin, the cuticle layer contributes relatively more to its physical properties.6 As hair grows, the cell layers of the cuticle are progressively eliminated and the further they are from the scalp, the more their quality and numbers are reduced, thereby weakening the capillary stems. The various types of attack described above speed up this natural process, raising the cuticle scales, which then lose their faculty to be flattened and therefore no longer ensure protection.
As a result, the hair becomes porous and avidly absorbs liquids but can no longer retain them, which leads to a loss of vital elements such as water and lipids. The lifted scales also hamper proper sebum diffusion along the capillary stem and the hair becomes dry. Damaged hair may have uplifted cuticles as well as swollen, eroded and brittle cuticles, or may have lost them altogether. Further, holes and microfissures can appear along the stem.
The disappearance of the cuticle on hair ends leaves the cortex exposed and without protection, hair ends literally explode and divide into small units—although in some cases, damage to long bundles of bare keratin may not be as noticeable because its extrinsic properties are still present in spite of the extensive damage. For instance, Robbins and Crawford reported that up to six treatments with 15.4% diperisophthalic acid had no effect on hair traction properties but observation under a microscope showed extreme swelling of the cuticle.10
The keratin fibrils in hair fibers break up and lose fragments of amino acids, including those containing sulfur. The keratin chains lose their elasticity and resistance and begin to bristle and curl up into what are known as split ends, and when a hair fiber is extensively damaged, it ends up breaking. Brittle hair can break at any point along the fiber, including right next to the scalp, thereby diminishing the overall volume of hair. However, this reduction is only temporary and new hair will not bear the marks of previous damage.
Hair Repair Serum
Shiny, smooth hair is perceived to be healthy. In fact, this physical appearance is indicative of the outer, intensely hydrophobic layer combined with the integrity of the cortex, conferring properties of luster and volume.11 Although the hair stem is composed of dead cells, they consist of proteins and lipids that can be repaired but once hair is damaged, traditional shampoo and conditioner formulas are not sufficient; hair requires extra, particularly mild care to recover shine and health on several levels,12 i.e., from the middle of the cortex to the cuticle. Film-forming agents such as silicones often are used in repair treatments because they alter hair surface properties, imparting smoothing and gliding effects and shine, and have a significant impact on the macroscopic behavior of hair assembly.13 By design, however, they cover hair fibers with a fine, waterproof layer that can slow or prevent the penetration of actives.
In addition, more consumers are following the worldwide ecological trend and are concerned over the impact these products may have on their personal well-being and/or the environment. For instance, in January 2009, Environment Canada and Health Canada concluded that silicones D4 and D5, although not harmful to human health, accumulate in and may be toxic for the environment.14 But while consumers want products containing ingredients that are as ecological as possible, this must not be at the detriment of the product’s performance.
In consideration of these requirements, a hair treatment serum based on natural actives and omitting film-formers was formulated (consisting of Viola Tricolor Extract, Cetearyl Alcohol, Gossypium Oil, Orbignya Speciosa Kernel Oil, Astrocaryum Murumuru Seed Butter, Isodecyl Neopentanoate,Caprylic/Capric Triglyceride and Tocopherol) and its repair capabilities examined. The microscope observations described here were made preliminary to other comparative and consumer tests.
Reconstituting Deficient Hair Matter
As described previously, when hair is damaged, the keratin chains have lesions and are missing amino acids that serve as the chain links. In order to replace these damaged chains, a complex of 18 free amino acids derived from wheat, corn and soy proteins was developed in specific and defined proportions to mimic the natural composition of keratin. For instance, the high sulfur amino acid content of the soy is similar to that of human hair and wool, with one of every five residues being half-cysteine.15, 16
To correct hydration, low molecular weight (LMW) hyaluronic acid, a disaccharide polymer, was utilized. Hyaluronic acid (HA) has perfect biocompatibility and is highly hygroscopic, having the capacity to retain up to a 1,000 times its own weight in water. Depending on its molecular weight, the penetration and mode of action of the hyaluronic acid used will vary. In this case, LMW was used so that it could be taken up into the heart of the cortex of the capillary stem to capture and retain water. A penetration test of bleached and untreated hair confirmed that a fluorescently labeled HA solution was absorbed into the damaged section of hair (data not shown).
To repair microlesions, ceramides extracted from rice bran, i.e., fragments of rice grain husks, also were included. These materials are analogous to the lipids found in cuticle cells and therefore are uniformly absorbed between cuticles, acting as intercellular cement to seal the scales and fill in gaps. To further increase their substantiveness, the ceramides were encapsulated in positively charged, biodegradable microspheres thanks to the association of a cationic polymer, in this case one derived from honey and chitosan. This combination gives the ceramides a high affinity for negatively charged areas such as hair keratin to maintain a dosed reconstitution activity over time. Once they bind to the hair surface, the microspheres open and release the encapsulated active in their most active form to the targeted area, i.e., the spaces left empty by the original ceramides. A fluorescent wash test was performed and confirmed the substantivity of the spheres (data not shown).
Considering split ends, two additional actives were employed to address the most damaged parts of the capillary stem and prevent split ends. First, silk peptides have a high affinity for keratin and form a filmogenic network on hair ends; however, due to their molecular weight, they do not form films as silicones do. These networks act where the fiber has been damaged by reassembling the dissociated elements of split end. The hair ends thus appear regular and uniform and feel soft.
In addition, Brazilian palm oils (INCI: Orbignya Speciosa Kernel Oil (and) Astrocaryum Murumuru Seed Butter) were used to replenish lipids and overcome the rough look of damaged hair and split ends by imparting shine and softness. In vitro and in vivo studies were conducted and showed an improvement in raised cuticles and irregularities (data not shown).
Having low molecular weights, all these constitutive elements were designed to deeply penetrate the hair fiber and act as a filler to occupy the space of the lost keratin, interlocking and thus filling structural gaps.
Materials and Methods
In order to observe the efficacy of the serum, it was applied to damaged split ends and the effects were observed under a microscope. To produce the damaged hair, five hair strands were washed with a 12% solution of sodium lauryl ether sulphate (SLES) (pH 6.5) for 15 min, followed by rinsing three times for 2 min with clear water. The hair strands were then bleached with a solution of 5% hydrogen peroxide (pH 9.4) for 20 min and rinsed abundantly with water. Finally, the strands were dried for 30 min with hot air (~ 55°C) and observed with a binocular microscope to identify the most damaged, split hair fibers.
The fibers were placed for analysis by field emission gun scanning electron microscopy (FEGSEM)a using an electron acceleration voltage of 1 kV with non-metallized samples and examined for the presence of splits on the stems and ends. The hair fibers were then treated one by one with the serum and dried with hot air (~ 55°C).
Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6 show that after treatment, the damaged stems and ends previously identified were significantly improved. These preliminary tests were followed by others, including a test of 61 women (26–50 years) who applied the treatment two to three times daily for two weeks and found the same results (data not shown). Based on these findings, a commercial serum capable of reforming the integrity of hair was launched.
The technical novelty of this project is linked to the development of a capillary treatment formulated with natural actives that ensure the sustained integrity of the capillary fiber while bringing remarkable shine without the use of silicones. Examination under the electron microscope allowed the state of the hair fibers to be checked before and after treatment and the efficiency of the serum to be confirmed.
- SS Sandhu and C Robbins, A simple and sensitive technique, based on protein loss measurement, to assess surface damage to human hair, J Soc Cosmet Chem 44 163–175 (1993)
- AC Santos Nogeuria and I Joekes, Hair color changes and protein damage caused by UV radiation, J Photochem Photobiol B Biol 74 109–117 (2004)
- S Nagase et al, Correlation of visual perception mechanism of hair appearance, proceedings of the 12th International Hair Science Symposium, Heidelberg, Germany (Sep 5–7, 2001)
- M Okamato et al, Influence of internal structure on hair fiber appearance, III Generation of light scattering factors in hair cuticles and the influence on hair shine, Cosmetic Science 54, 353–366 (2003)
- F Bell et al, Biophysical and mechanical response of keratinous fibres to changes in temperature and humidity, J Cosmet Sci 55 S19–S24 (2004)
- D Persaud and YK Kamath, Torsional method for evaluating hair damage and performance of hair care ingredients, J Cosmet Sci 55 S65–S77 (2004)
- C Dubief, Experiments with hair photodegradation, Cosm & Toil 107(10) 95–102 (1992)
- S Ratnapandian et al, Photodegradation of human hair, J Cosmetic Sci 49 309–320(1998)
- SB Reutsch et al, Photodegradation of human hair: An SEM study, J Cosmetic Sci 51 103–127 (2000)
- CR Robbins and RJ Crawford, Cuticle damage and the tensile properties of human hair, J Soc Cosmet Chem 42 59–68 (1991)
- R Sinclair, Healthy hair: What is it? J Investigative Dermatology Symposium Proceedings 12 2–5 (2007)
- KV Brown, Damaged hair has a different affinity for hair products, in Hair and Hair Care, 1st edn, DH Johnson, ed, Marcel Dekker, New York (1977) pp 191–215
- A Dussaud and L Fieschi-Corso, Influence of functionalized silicones on hair fiber-fiber interactions and on the relationship with the macroscopic behavior of hair assembly, J Cosmet Sci 60(2) 261–271 (Mar-Apr 2009)
- Environment Canada and Health Canada Proposed Risk Management Approach for Cyclotetrasiloxane, cotamethyl- (D4) and Cyclopentasiloxane, decamethyl- (D5), available at www.ec.gc.ca/substances/ese/eng/challenge/batch2/batch2_541-02-6_rm.cfm (Accessed Nov 16, 2011)
- M Friedman and DL Brandon, Nutritional and health benefits of soy proteins, J Agric Food Chem 49 (3) 1069–1086 (2001)
- M Friedman and R Orracah-Tetteh, Hair as an index of protein malnutrition, in Nutritional Improvement of Food and Feed Proteins, M Friedman, ed, Plenum, New York (1978) pp 131–154