18-MEA and Healthy Hair
Human hair is primarily protein, with lipids and melanin making up a majority of the remainder. The hair fiber is a shaft-like structure, as depicted in Figure 1, and consists of a cortex, a cuticle and a medulla. The cortex is a cylinder-like structure comprised of long, spindle-shaped cortical cells and constitutes the major portion of the fiber's mass. The cuticle is a thin laminar-like structure comprised of layers of overlapping, flat scale-like cells. The cuticle constitutes the outer surface area of the hair fiber and surrounds the cortex, acting like a protective sheath. Because it is the visible area of the hair, the cuticle also gives hair its optical properties (e.g., shine, gloss).
Sandwiched in between the overlapping cuticle cells is a multi-component layer known as the cell membrane complex (CMC). Sometimes referred to as the epicuticle, the CMC cements the cuticle together and binds it to the cortex, thus becoming the top layer of one cuticle cell and the bottom layer of the one directly beneath it. Most of the evidence to date suggests that the CMC is comprised of a glycoprotein δ-layer pressed between two β-layers, as shown in Figure 2.3 The primary lipid, 18-methyl eicosanoic acid (18-MEA), is found in the upper β-layer, along with oleic and palmitic acid. This primary lipid is responsible for giving hair its natural hydrophobicity, as it coats the surface of abutting cuticle cells. When a cuticle is removed, 18-MEA becomes exposed and coats the newly exposed cuticle surface. This contributes to the hair’s wet and dry combing properties as the presence of, 18-MEA makes hair easier to comb.
Environmental factors and chemical treatment as well as everyday grooming processes can have an adverse effect on the integrity of 18-MEA. Although 18-MEA and the other hair surface lipids appear to be resistant to extraction with organic solvents, they can be removed readily by alkaline hydrolysis. This suggests that the use of high pH products, such as perms, hair dyes or hair relaxers, could deplete these important lipids from the hair surface. Studies on wool fibers have shown that exposure to natural, or artificial, weathering or UV irradiation increases the hydrophilicity and wettability of fibers.4 Additionally, exposure to UV irradiation has also been shown to deplete wool of its lipid content. Of the fatty acids, 18-MEA appears to be lost to the greatest extent; therefore, hair it is necessary to restore18-MEA to maintain healthy hair.
It has been found that Cutissential Behenyl 18-MEA (INCI: Behentrimonium Methosulfate (and) C10-40 Isoalkylamidopropylethyldimonium Ethosulfate (and) Cetyl alcohol) and Cutissential 18-MEA 40 (INCI: C10-40 Isoalkylamidopropylethyldimonium Ethosulfate (and) Dipropylene glycol ) can help replenish the 18-MEA that is depleted from the hair surface.
Average Dynamic Advancing Contact Angle
The dynamic advancing contact angle is a measurement used to determine hair’s hydrophobicity. “Healthy” undamaged hair is hydrophobic (water repelling). When chemical, environmental or mechanical damage occurs, it will exhibit a more hydrophilic (water loving) nature. If a product can restore hair to a more hydrophobic state, it can be concluded the hair is “healthier.” The dynamic advancing contact angles of virgin and bleached hair samples were measured before and after treatment with a 1.5% active solution of Cutissential Behenyl 18-MEA, and shampoo bases (ALS-1 and SLS-1) containing 1.5% active Cutissential 18-MEA 40. The relative change in the degree of the contact angle, as compared to untreated hair, is represented in Figure 3.
There was virtually no change in contact angle for the treated and untreated virgin hair and Figure 3 shows the dynamic advancing contact angle results of bleached hair. The significant difference observed with bleached hair, shows the hydrophilic nature of bleached hair and how severely damaging the bleaching process can be to the hair surface. The surface hydrophobicity of the bleached hair fibers is improved after treatment with Cutissential Behenyl 18-MEA or Cutissential 18-MEA 40, restoring damaged, bleached hair to a more natural, healthy state.
Fluorescence Micrographs of Hair Fibers
Fluorescence micrographs of hair fibers measure the amount of cationic material, such as 18-MEA, present on the hair surface. Fluorescence micrographs of bleached hair fibers treated with and without a 1.5% active solution of Cutissential Behenyl 18-MEA are shown in Figure 4a and Figure 4b, respectively. In addition, bleached hair fibers treated with either SLS-1 shampoo alone or SLS-1 conditioning shampoo containing 1.5% active Cutissential 18-MEA 40 are shown in Figure 5a and Figure 5b, respectively.
From the high fluorescence intensity of the hair fiber, shown here in green in Figure 4b and Figure 5b, it is apparent that Cutissential Behenyl 18-MEA and Cutissential 18-MEA 40 were effectively deposited onto the hair. In the fluorescence micrographs shown in Figure 4a and Figure 5a, there is little evidence of green, indicating that virtually no cationic material was detected on the hair surface. Fluorescence micrographs of the hair fibers treated with the ALS-1 shampoo alone and the corresponding conditioning version gave similar results.
The addition of Cutissential Behenyl 18-MEA or Cutissential 18-MEA 40 to hair care formulations can restore the healthy appearance of the hair, as they allow for a substantive replenishment of 18-MEA to the hair fiber and enhance the overall hydrophobicity of the hair itself. Both are suitable for leave on and rinse off conditioners, styling products, treatments and more. Cutissential 18-MEA-40 has also been shown to be effective in shampoo systems.