Conventionally, the medical focus has been either on hair loss or the condition of the scalp in terms of specific dermatological conditions. In fact, the proximate structural arrangement of the scalp and hair leads to an interdependent relationship between the two. The protective benefits of the hair to the scalp, such as ultraviolet radiation (UVR) screening, moisture retention, and mechanical shielding, are obvious, while the role of the scalp as an incubatory environment for the preemergent hair fiber is often overlooked.[3]
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Aging of the hair itself affects hair color (graying), hair production (alopecia), and structural properties of the hair fiber (hair diameter, hair fiber curvature, stretching, bending, and torsional rigidity of the hair fiber, and lipid composition), with its consequence for the manageability and overall appearance of hair.[37]
In contrast, the aging effects on nonbalding scalp are relatively unnoticed. Underneath the hair, the scalp may appear pale and dry, with a certain degree of laxity. In contrast, balding scalp exhibits the features of photo-aged skin, including irregular pigmentation, wrinkling, atrophy, telangiectasia, and findings of cutaneous premalignant and malignant diseases, such as actinic keratosis, basal cell carcinoma, and squamous cell carcinoma. Onset of solar elastosis of the scalp precedes the onset of hair loss in androgenetic alopecia,[38] providing the evidence that scalp hair does not completely protect from the effects of UVR and the need for added scalp UVR protection. Other aging features seen in the sun-damaged scalp include variability in thickness and cellularity in epidermis, unevenly distributed melanocytes, and increased inflammatory cells in the dermis. Due to the decrease in volume and elasticity, the skin becomes thinner and more easily damaged. Moreover, aging skin receives less blood flow and exhibits lower glandular activity. The net result of these effects is the decreasing ability of skin to heal itself, with an increase of skin pathologies.
The condition of the hair fiber must be viewed as the result of a combination of preemergent and of postemergent factors.[41] Sources of oxidative stress with impact on the preemergent fiber include oxidative metabolism; smoking;[42,43] UVR;[44] inflammation from microbial, pollutant, or irritant origins; and oxidized scalp lipids. Sources of oxidative stress with impact on the postemergent fiber include again UVR, and chemical insults from oxidizing hair colorants and pollutants [Figure 1].[41]
Studies have demonstrated oxidative stress associated with alopecia.[49,50,51,52,53,54] The measures are similar to those in other skin conditions: antioxidant enzymes, protein oxidation, and lipid oxidation. The most common manifestation of the oxidative stress is lipid oxidation, and therefore quantitation of lipid peroxidation is a particularly prevalent method in dermatologic research.[7] The oxidized lipids are now understood to negatively influence the normal growth of hair: Naito et al.[55] analyzed the effect of the lipid peroxides on hair follicles and observed that the topical application of linolein hydroperoxides, one of the lipid peroxides, leads to the early onset of the catagen phase in hair cycles. Furthermore, they found that lipid peroxides induced apoptosis of hair follicle cells. They also induced apoptosis in human epidermal keratinocytes by upregulating apoptosis-related genes. These results indicate that lipid peroxides, which can cause free radicals, induce the apoptosis of hair follicle cells, and this is followed by early onset of the catagen phase.
As can be seen from the summary of scalp abnormalities, the most common manifestation to hair emerged from an unhealthy scalp is an altered cuticle with evidence of surface pitting, roughness, cuticle rigidity, or breakage. In some cases, the impact is manifested as shine reduction. In addition to the physical changes, there are biochemical alterations observed in hair emerged from an unhealthy scalp, with both protein and lipid components affected, most commonly by oxidative damage.[17,61,66,67]
Ultimately, shampoo treatments are the most commonly used means of managing hair and scalp conditions and have proven to be effective for the treatment of dandruff and seborrheic dermatitis,[79,80,81,82,83] psoriasis,[84] and atopic dermatitis of the head-and-neck type.[85,86] Today, it is understood that scalp care products for dandruff and seborrheic dermatitis, psoriasis, and atopic dermatitis exert their benefits by controlling scalp Malassezia levels.
Given the observations on the role of oxidative stress in premature hair loss and the part that Malassezia spp. play in generating oxidative stress, it is likely that products with Malassezia control active would exert some hair loss prevention benefits.
A 37-year-old man with seborrheic dermatitis and hair loss in the vertex (a) before, and (b) after 3 months successful treatment with anti-dandruff shampoo with antimycotic activity (personal observation)
The cell membrane complex (CMC) is intercellular matter. CMC consists of cell membranes and adhesive material (cement) binding the cell membranes between two cuticle cells, two cortical cells and cuticle-cortex cells. The most important layer of the CMC is called the beta-layer, and it is considered to be the intercellular cement and it is sandwiched by other layers from each cell. The CMC and the endocuticle are very vulnerable regions to the chemical treatments such as bleaching, dyeing and hair straightening/perm procedures. Also, the everyday grooming and shampooing friction may disrupt the CMC.[3,4,5]
CMC fractures may be seen before the hair fiber is ruptured. The exposure to repeated rough washing, unprotected drying, friction actions, sunlight and alkaline chemical treatments lead to a decrease in the lipid content of the cell surface changing it from the state of hydrophobicity to a more hydrophilic, negatively charged surface.[3,4,5,6]
It is common to use cationic ingredients in many shampoos' formulations with anionic surfactants in order to result in charge neutralization forming a cationic-anionic complex, a neutral hydrophobic ingredient. Therefore, we can understand that the interaction between the ingredients is more important than the ingredient alone, as we are led to believe by the media. It is very common to think that a new release product that contains a certain ingredient has the magic ability to transform dull hair into shiny and smooth hair. Most of the time, the major ingredients do not change, and sometimes the capacity of the ingredients to interact inside the shampoo's or conditioner's chassis or system is what makes the product acts better. Bleached and chemical treated hair have a higher affinity to conditioning ingredients because they have a low isoelectric point (higher concentration of negative sites) and are more porous than virgin hair.[5,20]
Dimethicone is the most widely used silicone in hair care industry, and entropy is important for its adsorption to the hair surface. Dimethicone is the main ingredient of the two-in-one shampoos. Others are: Aminosilicones, siloxysilicates, anionic silicones and others. They differ on deposition and solubility in a water medium, therefore acting differently on the hair. Some silicones can even enhance the shine of hair fiber by reflecting the light. Dimethicone has the effect of protecting the hair shaft from abrasive actions while siloxysilicates increase hair body.[5,21,22,23]
Polysiloxane polymers may re-cement lifted cuticle scales and prevent damage from heat. Amino functional silicones are cationic substances but not necessarily are more substantive to the hair than dimethicone, depending on the size of the molecule and the charge of the system. Dimethicones are hydrophobic, so they adsorb better on virgin hair and root rather than tips. To enhance the deposition of dimethicone on chemical treated and damaged hair the products use cationic bridging agents which act increasing affinity between hair and the silicone.[4,5,12,24,23]
Other polymers are the polypeptides and proteins for they are very substantive to the hair for having many ionic and polar sites for bonding and are large molecules to attach to the hair surface (van der Walls force). Small molecules can even diffuse into hair (
Oils play an important role in protecting hair from damage. Some oils can penetrate the hair and reduce the amount of water absorbed in the hair, leading to a lowering of swelling.[26] This can result in lower hygral fatigue (repeated swelling and drying), a factor that can damage hair. The oil can fill the gap between the cuticle cells and prevent the penetration of the aggressive substances such as surfactants into the follicle. Applying oil on a regular basis can enhance lubrication of the shaft and help prevent hair breakage. Rele and Mohile in 2003, studied the properties of mineral oil, coconut oil and sunflower oil on hair.[27] Among three oils, coconut oil was the only oil found to reduce the protein loss for both undamaged and damaged hair when used as a prewash and postwash grooming product. Both sunflower and mineral oils do not help in reducing the protein loss from hair. This difference in results could arise from the composition of each of these oils. Coconut oil, being a triglyceride of lauric acid (principal fatty acid), has a high affinity for hair proteins and because of its low molecular weight and straight linear chain, is able to penetrate inside the hair shaft. Mineral oil, a hydrocarbon, does not penetrate. Sunflower oil is a triglyceride of linoleic acid with a bulky structure and double bonds and has limited penetration to the fiber, not reaching the cortex. The mineral oil and the sunflower oil may have a film effect and adsorb to the surface of the cuticle enhancing shine and diminishing friction and for these, avoid hair damage.[22]
Keis et al. in 2005 studied the effect of coconut oil, olive oil, sunflower oil and mineral oil on the hair.[28] Except for mineral oil, heat decreased the capillary adhesion of the other oils, resulting from the penetration into the hair fiber by diffusion, leaving a thin film on the surface. Although thick films of oil can mask the lifted scales of the cuticle, it may leave an oily and heavy look to the hair. It is preferred to reapply oils that leave a thin layer on the surface and are well absorbed by the fiber. In 2009, the Brazilian oils and butters were studied by Fregonesi et al.[29] They analyzed the following substances: Passion fruit seed (77% linoleic acid), Brazilian nut (38% oleic acid and 35% linoleic acid), palm olein (47% oleic acid), buriti (79% oleic acid), palm stearin (42% palmitic acid and 41% oleic acid), tucumã (48% lauric acid and 27% myristic acid), ucuúba (75% myristic acid), sapucainha (47% chaulmoogric acid, 27% hydnocarpic and 19 gorlic acid). Oil treatment reduced the combing force percentage for wet conditions. However, the hair treated with butters showed poor combing. Treatments using oils reduced the formation of split ends in the hair. Tresses treated with Brazilian nut and mineral oils gave the lowest formation of split ends.[29] 2ff7e9595c
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