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Chemical and Physical Properties of Emollients
Abstract
Emollients are essential ingredients in all types of skin care products. The selection of the emollient phase will determine skin feel, moisturization capacity, and stability of the formulation. Emollients can be classified according to their chemical composition or by their physicochemical properties. The basic building blocks of most emollients are long chain hydrocarbons, often combined with alcohols and acids in the form of esters. The raw materials are derived from petrochemical or natural sources, such as vegetable oils and fats.
By varying the molecular structures and the composition of the emollients, properties such as rheology and polarity can be adjusted to meet the requirements on moisturization, sensory properties, and delivery of actives. The rheological properties of the emollient can influence the lubricity and spreading properties of the formulation. The polarity of the emollient is linked to the delivery of actives and to the interaction between the formulation and skin.
When selecting emollients for a formulation, the stability in terms of hydrolysis and oxidation must be considered. Esters can be hydrolyzed to the corresponding alcohol and acid if the formulation is too acidic or alkaline. Oxidation will produce off-flavors and can also lead to the formation of inflammatory and irritating breakdown products.
The selection of an emollient mixture for a formulation must also consider parameters such as purity, biodegradability, and sustainability, leading to the development of new processes and types of emollients in the future.
... In terms of sensory evaluations, it showed high values of glossiness, residue and oiliness. Usually used to stabilize emulsions, alcohols can also be used as emollients when added between 1% and 2% [5,6]. ...
... Note that triglycerides can also be synthesized from glycerol and fatty acids (e.g. caprylic/ capric triglycerides) [5]. ...
... When combining Eq. (3) with Young's equation (Eq. (4)), the spreading coefficient is finally expressed as a function of surface properties: surface tension (γ) and contact angle (θ) in Eq. (5). ...
Thirteen current commercial emollients from different chemical families (hydrocarbon, ester, ether, and silicone) were firstly characterized by eight physicochemical properties which were a-priori thought to be strongly related to sensory perception. Those include usual properties as well as more original ones such as volatility, estimated by the evaporated mass fraction during a fixed duration, as well as the polar and dispersive components of the surface tension. Principal Component Analysis and Hierarchical Agglomerative Clustering led to a partition of the emollients into groups that matched fairly well with the different chemical families. It also helped to highlight the main characteristics of each group. As expected, silicone had the lowest surface properties. Hydrocarbons showed the highest volatilities and the lowest viscosities. Esters mainly displayed the highest surface properties, and within this group, diesters showed higher polar components than monoesters. Sensory evaluation was performed at the same time by a professional panel. The sensory attribute “Spontaneous spreading” was found to be larger for silicone and hydrocarbons than for esters and ether. From our set of data, a suitable correlation was obtained between the sensory attribute “Spontaneous spreading” and the calculated spreading coefficient on Teflon® which combines surface tension with the cosine of contact angle.
... Emollients constitute the largest ingredient group (volume-wise) in skin care products and are generally responsible for the main carbon emission contribution. They can comprise between 5 to 30% of an oil-in-water formulation [27]. Emollients are used to soothe and maintain hydration of the skin through creating a hydrophobic protective The beauty of fermentation and the incredible potential in skin care is related to the enormous portfolio of ingredients that can be synthesized by microorganisms and be suitable for a wide range of cosmetic products. ...
... Emollients constitute the largest ingredient group (volume-wise) in skin care products and are generally responsible for the main carbon emission contribution. They can comprise between 5 to 30% of an oil-in-water formulation [27]. Emollients are used to soothe and maintain hydration of the skin through creating a hydrophobic protective layer that prevents water loss. ...
The cosmetic segment is a rapidly growing industry that has been challenged in recent years due to the origin and impact of its ingredients and manufacturing techniques. With a focus on reducing carbon dioxide emissions and improving the degradability of products, many conventional ingredients are being dismissed to meet more exigent regulations and consumer ethical demands. Biotechnology, and fermentation as the core technology, is a solution to support and drive more sustainable growth for the cosmetic industry. This review presents the latest research and development in fermentation applied to cosmetics and showcases multiple examples throughout all classes of ingredients: from functional compounds, such as oil and surfactants, to multi-faceted molecules with a wide spectrum of formulations and skin benefits derived from their emulsifying, antimicrobial or antioxidant properties. The bottlenecks associated with the commercialization of such ingredients, together with successful examples, are also discussed. The shift towards a bio-based beauty industry requires a combination of technical, regulatory and marketing efforts. Fermentation strategies to better utilize low-cost substrates and optimize microorganisms and processes will reduce overall costs, reducing the price gap with traditional methods of production. The testing, standardization and regulation of these new ingredients need to catch up with the fast research happening in the field. Finally, consumer communication is key to achieve a successful introduction of biotech ingredients in the market.
... Due to high viscosity (η = 28.1 mPa s) and nonvolatility (Т b = 350°C) squalane manifests the occlusive behavior, facilitating strengthening of the barrier functions of the skin. Essential oils represent the most important group of chemical compounds used as emollients [87][88][89]. A great diversity of initial acids and alcohols entails a wide variety oils which explains their common use in cosmetic products. ...
... Les substances humectantes : substances ayant des propriétés hygroscopiques, qui ➢ Les substances émollientes : laissent un film huileux à la surface de la peau, ce qui permet d'en maintenir la flexibilité (2-octyldodecanol, acide oléique, acide isostéarique, myristate d'isopropyle, glycérol…)(38). ...
L’acné est l’affection dermatologique la plus commune touchant 80 % de la population âgée entre 11 et 30 ans. Les anti-acnéiques les plus efficaces
sont les rétinoïdes et le peroxyde de benzoyle. Cependant, l’un de leurs effets indésirables les plus remarqués est la xérodermie, appelée aussi
xérose ou sécheresse cutanée, qui peut affecter la qualité de vie du patient surtout quand elle se situe au niveau du visage.
L’objectif principal de cette étude est de recenser les remèdes naturels utilisés par les acnéiques en Algérie pour traiter la xérodermie et de justifier,
par une étude bibliographique, l’usage de ces remèdes.
Il s’agit principalement d’une étude descriptive transversale, la collecte des données est faite à travers un questionnaire en ligne. Les critères
d’inclusion sont : la résidence en Algérie, l’atteinte d’acné et le traitement par des anti-acnéiques. Les remèdes recensés ont fait l’objet d’une
recherche bibliographique.
L’échantillon est constitué de 185 personnes dont 35,1 % ont eu recours à l’utilisation d’un remède naturel. 31 remèdes ont été recensés, les plus
cités sont : l’huile d’olive, le gel d’Aloe vera et le miel .95,4 % ont considéré le remède naturel comme étant efficace dont 44,6 % ont remarqué
une amélioration juste après quelques jours d’utilisation.
Selon la bibliographie, l’huile d’olive a une composition similaire au sébum. Quant à l’aloe vera, il a été démontré que son extrait lyophilisé à
différentes concentrations a significativement amélioré l’hydratation cutanée par rapport au contrôle. D’autre part, le miel est inclus dans « the
International Nomenclature of Cosmetic Ingredients » (INCI) et il est classé comme un produit émollient, humectant et hydratant.
Cette étude nous a permis de recenser les remèdes naturels utilisés traditionnellement pour traiter la xérodermie, la bibliographie a pu confirmer
ces usages. Ceci pourrait donc constituer une base de données intéressante pour les laboratoires pour de nouvelles recherches et formulations.
... This increase of intermolecular attraction is also felt in the sensory properties of the material. As the attraction between the molecules increases, more force has to be applied in order for the layers of molecules to slide against each other, leading to lower spreadability and a heavier feel (Alander, 2012). ...
... • Nacinamida (nicotinamida): amida del ácido nicotínico, vitamina del complejo B hidrosoluble, que actúa como precursora del dinucleótido de nicotinamida y adenina (NAD) y de su fosfato (NADP), coenzimas esenciales para las reacciones redox del metabolismo energético celular. Estimula la síntesis lipídica y la diferenciación queratinocitaria en preparaciones tópicas junto a glicerol 19 . ...
espanolUn anciano es una persona de mucha edad que puede identificarse a simple vista por el estado de su piel y su cabello. En la piel del anciano, se producen, entre otros, una serie de cambios epidermicos —en los queratinocitos, las celulas de Langerhans y los melanocitos— que favorecen la piel seca, las infecciones y las alteraciones tanto de la inmunidad como de la pigmentacion. En la dermis, disminuye la funcion de los fibroblastos, lo que lleva a la mengua del soporte cutaneo y, por lo tanto, propicia las arrugas. La higiene con jabones de pH acido (5,5) y aditivos grasos (syndets), la hidratacion topica con principios activos seleccionados y la fotoproteccion farmacologica representada por los filtros solares son la base del cuidado de la piel del anciano. A estos pilares se puede anadir un tratamiento correctivo de las arrugas y manchas con cosmeticos y cosmeceuticos reparadores. Las unas requieren un cuidado especial por su frecuente infeccion por hongos. EnglishAn elderly man or woman is an old aged person, who can be identified at first sight by the state of his/her skin and hair. In the skin of the elderly are, amongst others, a series of changes-epidermal keratinocytes, Langerhans cells and melanocitos favoring dry skin, infections, and impaired immunity and pigmentation. In the dermis, the fibroblast function decreases, leading to the decline of cutaneous support and, therefore, promoting wrinks. Hygiene with acid pH (5.5) and fatty additives (syn-dets) soap, topical moisturizing with selected active ingredients and pharmacological photoprotection represented by sunscreens are the basis of skin care in the elderly. To these pillars a corrective treatment of wrinkles and blemishes can be added with cosmetics and cosmeceuticals repairers. Nails require special care because of their frequent fungal infection.
... One of the problems that have been observed in pharmaceutical compositions during stability tests is the esterification of the carboxyl groups in the presence of ethanol (13). In some cases, the interaction is beneficial (14,15), but it typically leads to the formation of undesirable substances in the final product (16). ...
The identification of new contaminants is critical in the development of new medicinal products. Many impurities, such as pentanedioic acid, hexanedioic acid, heptanedioic acid, octanedioic acid, decanedioic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid, have been identified in samples of azelaic acid. The aim of this study was to identify impurities observed during the stability tests of a new liposomal dosage form of azelaic acid that is composed of phosphatidylcholine and a mixture of ethyl alcohol and water, using high-performance liquid chromatography with evaporative light-scattering detector (HPLC-ELSD), gas chromatography-flame ionisation detection (GC-FID), and gas chromatography-mass spectrometry (GC-MS) methods. During the research and development of a new liposomal formulation of azelaic acid, we developed a method for determining the contamination of azelaic acid using HPLC-ELSD. During our analytical tests, we identified a previously unknown impurity of a liposomal preparation of azelaic acid that appeared in the liposomal formulation of azelaic acid during preliminary stability studies. The procedure led to the conclusion that the impurity was caused by the reaction of azelaic acid with one of the excipients that was applied in the product. The impurity was finally identified as an ethyl monoester of azelaic acid. The identification procedure of this compound was carried out in a series of experiments comparing the chromatograms that were obtained via the following chromatographic methods: HPLC-ELSD, GC-FID, and GC-MS. The final identification of the compound was carried out by GC with MS.
Emollients are multifunctional, water-insoluble ingredients used in cosmetic products. This study aims to define the chemical and physical characteristics and test the activities of a new ester-based emollient, Sharofeel DS (DS), in comparison with other commonly used emollients (fatty alcohols, esters, and silicone emollients). The new entity was synthesized from naturally derived reactants and designed to be utilized in different cosmetic applications, such as skin care, hair care, and makeup. Methods: The emollient was characterized on the basis of its physical properties (Ultraviolet/Infrared (UV/IR) analysis, density, dynamic viscosity, refractive index, surface tension, and contact angle), calorimetric properties by thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC), viscoelastic properties as is and in emulsion, and toxicity tests. According to the results obtained, DS demonstrated density (0.881 g/mL) and viscosity (86 cPs) values comparable to fatty alcohol emollients, with a refractive index (1.457) comparable to fatty alcohol and ester-based emollients and a surface tension (22.53 mN/m ± 0.11 mN/m) similar to the ester-based ones. It proved stable below 308 °C and capable of reducing the loss of internal water from hair strands (−7.5% w/w). Lastly, the toxicity tests proved that DS is safe for topical skincare, haircare, and makeup applications.
The structural diversity of organosilicon compounds used in decorative and care cosmetic products is studied. The unique physicochemical properties of silicones allowing their application as emollients, moisturizers, emulsifiers, film formers, viscosity regulators, and antistatic and binding agents are described. Mechanisms of action of various structure silicones, due to which organosilicon compounds are advantageously used to impart certain properties to cosmetic products, are demonstrated. A comparative analysis of the efficiency of silicones versus natural compounds serving similar functions in cosmetic products is performed. The issue of silicone safety for human health is considered.
The targeted choice of the emollient of a cream determines its physicochemical properties and clinical effectiveness. This work researched the effects of emollient properties on the final characteristics and potential
performance of oil-in-water dermatological creams. Seven emollients with different chemical characteristics and
structures (alkane, triglyceride, ether, silicone, vegetable oils, and mineral oil) were tested in a model formulation. Early stability, pH, droplet size distribution, rheology, tackiness, adhesivity, spreadability, tribology, and
release profile of a lipophilic substance model (in Franz cells, through a synthetic membrane, for six hours) were
assessed. The creams had acid epicutaneous pH and a “shear-thinning” “solid-like” viscoelastic behavior. Among
the seven emollients’ properties, polarity, density, and viscosity were the most influential. Droplet parameters
were the most impacted, pH and release were moderately affected, and the textural properties were lowly to
moderately impacted.
The emollient substitution in the model formulation affected the experimental parameters differently,
allowing formulation optimization and tailoring its potential therapeutic performance regarding drug release,
coadjutant effects, and dwell time on the skin. By looking at the creams’ characteristics, it was possible to select
the best-suited emollients for releasing a lipophilic drug, applying on painful skin, and formulation in wash-off
products or leave-on protective barrier creams.
There is an impairment of skin integrity derived from derangement of orthorhombic lateral organization caused by dysregulation of ceramide (CER) amounts in the skin barrier. The impaired skin barrier is replenished via CER, fatty acid, and cholesterol-containing nano-based formulations. However, it is still a challenge to formulate CER-containing-liposomes due to their chemical structure with poor aqueous solubility and high molecular weight. In this study, the design and optimization of CER-NP loaded liposomes are implemented by Response Surface Methodology (RSM) based on the quality-by-design approach. The formulation optimization process of liposomes containing CER-NP was carried out using the Design of Expert. The Central Composite Design was the design type with 3 factors at 5 levels: plus and minus alpha (axial points), plus and minus (factorial points), and the center point. The parameters were CER-NP, fatty acid, and cholesterol at 5 variable levels as independent variables. The responses were the particle size and PDI values of liposomes as responses which were measured using dynamic light scattering (DLS). The optimum formulation was selected based on mean particle size (136.6 ±4.05) and PDI values (0.248 ±0.012), and the prediction model success was evaluated based on the equation on the quadratic model. The encapsulation efficiency was clarified by sampling the CER-NP-loaded liposome with the centrifugal ultrafiltration method and analysis in high-
performance liquid chromatography (HPLC). The Cer-NP release from liposome was examined based on the in vitro release (IVRT). MTT assay was also performed on HaCaT human keratinocyte cell lines to assess the relative safety of the optimized liposomes loaded CER-NP. The experimental result (PS:136.6±4.05 nm and PDI: 0.248 ±0.012) and predicted result (PS:132.6 nm and PDI:0.278) were correlated. The CLSM image was conformable with the other studies and the encapsulation efficiency of CER-NP was 93.84±0.87%. The release profile was fitted with the Korsmeyer-Peppas model. The cytotoxicity studies showed that the liposomes for topical administration of CER-NP could be considered relatively safe. In conclusion, the optimized liposomes containing CER-NP could have the potential to restore the skin barrier function.
Keywords: Ceramide, liposome, skin barrier function, experimental design, topical administration
Marine macroalgae, such as Padina boergesenii, are gaining recognition in the cosmetics industry as valuable sources of natural bioactive compounds. This study aimed to investigate the biochemical profile of P. boergesenii and evaluate its potential as a cosmetic ingredient. Fourier-transform infrared (FTIR), gas chromatography–mass spectrometry (GCMS), and high-resolution liquid chromatography–mass spectrometry quadrupole time-of-flight (HRLCMS QTOF) analyses were employed to assess the functional groups, phycocompounds, and beneficial compounds present in P. boergesenii. Pigment estimation, total phenol and protein content determination, DPPH antioxidant analysis, and tyrosinase inhibition assay were conducted to evaluate the extracts’ ability to counteract oxidative stress and address hyperpigmentation concerns. Elemental composition and amino acid quantification were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) and HRLCMS, respectively. FTIR spectroscopy confirmed diverse functional groups, including halo compounds, alcohols, esters, amines, and acids. GCMS analysis identified moisturizing, conditioning, and anti-aging compounds such as long-chain fatty alcohols, fatty esters, fatty acids, and hydrocarbon derivatives. HRLCMS QTOF analysis revealed phenolic compounds, fatty acid derivatives, peptides, terpenoids, and amino acids with antioxidant, anti-inflammatory, and skin-nourishing properties. Elemental analysis indicated varying concentrations of elements, with silicon (Si) being the most abundant and copper (Cu) being the least abundant. The total phenol content was 86.50 µg/mL, suggesting the presence of antioxidants. The total protein content was 113.72 µg/mL, indicating nourishing and rejuvenating effects. The ethanolic extract exhibited an IC50 value of 36.75 μg/mL in the DPPH assay, indicating significant antioxidant activity. The methanolic extract showed an IC50 value of 42.784 μg/mL. Furthermore, P. boergesenii extracts demonstrated 62.14% inhibition of tyrosinase activity. This comprehensive analysis underscores the potential of P. boergesenii as an effective cosmetic ingredient for enhancing skin health. Given the increasing use of seaweed-based bioactive components in cosmetics, further exploration of P. boergesenii’s potential in the cosmetics industry is warranted to leverage its valuable properties.
Emollient oils are ubiquitous ingredients of personal care products, especially skin care and hair care formulations. They offer excellent spreading properties and give end-use products a soft, pleasant and non-sticky after-feel. Emollients belong to various petro- or bio-based chemical families among which silicone oils, hydrocarbons and esters are the most prominent. Silicones have exceptional physicochemical and sensory properties but their high chemical stability results in very low biodegradability and a high bioaccumulation potential. Nowadays, consumers are increasingly responsive to environmental issues and demand more environmentally friendly products. This awareness strongly encourages cosmetics industries to develop bio-based alternatives to silicone oils. Finding effective silicon-free emollients requires understanding the molecular origin of emollience. This review details the relationships between the molecular structures of emollients and their physicochemical properties as well as the resulting functional performances in order to facilitate the design of alternative oils with suitable physicochemical and sensory properties. The molecular profile of an ideal emollient in terms of chemical function (alkane, ether, ester, carbonate, alcohol), optimal number of carbons and branching is established to obtain an odourless oil with good spreading on the skin. Since none of the carbon-based emollients alone can imitate the non-sticky and dry feel of silicone oils, it is judicious to blend alkanes and esters to significantly improve both the sensory properties and the solubilizing properties of the synergistic mixture towards polar ingredients (sun filters, antioxidants, fragrances). Finally, it is shown how modelling tools (QSPR, COSMO-RS and neural networks) can predict in silico the key properties of hundreds of virtual candidate molecules in order to synthesize only the most promising whose predicted properties are close to the specifications.
Background
The emollients are important ingredients used in skincare formulations that can act as moisturizing agents through their occlusive potential, preventing skin water loss. Consumer interest in natural and sustainable products has grown considerably in the last few years, requiring efforts from the cosmetic industry to design products with raw materials of natural, organic and sustainable origin. Thus, it is essential to improve the knowledge about the behavior of cosmetic raw materials that can be used as sustainable alternatives to synthetic ingredients.
Aim
This work aimed to evaluate the occlusive performance of different vegetable oils used as emollients in skincare cosmetics, through comparative analysis with petrolatum, a synthetic emollient with a high occlusive skin potential.
Method
The study included 80 healthy female adult volunteers. TEWL measurements were performed before and after 15 minutes, 2 and 6 hours of emollients application on the forearms of the research participants. All research participants provided written informed consent.
Results
The results obtained showed that the vegetable oils were effective in providing an occlusive effect on the skin. When compared to the petrolatum, the vegetable oils did not provide a high immediate skin occlusion effect. However, most of them showed a skin occlusion performance comparable to petrolatum throughout the 6-hour time course.
Conclusion
Vegetable oils can be used as a sustainable alternative to synthetic emollients and they are promising in replacing petrolatum in skincare formulations with respect to the occlusion effect of the skin. The vegetable oils did not provide a high immediate skin occlusion effect (15 minutes post-application) as the petrolatum, which is known to have increased occlusion properties. However, most of them showed a skin occlusion performance comparable to petrolatum throughout the 6-hour time course.
A range of liquid emollient ester‐loaded body emulsions were evaluated on the basis of sensory profile, consumer perception, physicochemical, biometrological, and rheological performances. This was complemented by skin hydration and transepidermal water loss (TEWL) studies performed using a Corneometer® and Tewameter®, respectively. The rheological studies showed similar behavior of creams on variation of shear stress, frequency, and temperature. However, skin hydration performances of creams were found varied when compared between base cream and emollient ester‐containing creams. In case of the TEWL study, base cream (F1, no ester) and octyl palmitate‐containing cream (F2), exhibited the most protective behavior for the skin with minimal water loss. Sensory profiles of creams were obtained using the sensory descriptive analysis method. A study performed with human consumers (as subjects) using the difference of test attributes (directional) method showed the importance of sensory evaluation with consumers and proved to be an interesting analysis for comparison with the sensorial profile. In this case, the attributes with the highest intensity in the evaluated creams were, that is, spreadability, slipping, and dry touch. Stability studies of creams were performed for 90 days under different storage conditions. Stability studies showed octyl stearate‐containing (F2) and palmitate‐containing (F5) creams exhibited best stability under extended storage conditions. This research has demonstrated the importance of physicochemical characterization and sensory evaluations performed with consumers for more targeted analysis of cream‐based formulations to differentiate product characteristics and identify attributes‐led preferences.
Practical applications
Results from the present work suggest that emollients are directly responsible for sensory characteristics such as spreading, absorption, and touch on the skin; they can influence the viscosity and appearance of emulsions. After application on the skin, they regulate the moisture content of the epidermis together with the humectants. This research has demonstrated the importance of sensory evaluation, especially performed with consumers, which may be considered a more targeted analysis to differentiate product characteristics and help in the choice of emollient with the desired characteristics for the cosmetic product.
In recent years, sustainability on the cosmetics industry has received growing interest from consumers, cosmetics industries and organizations, as well as academics from various disciplinary fields. Increasing concerns about cosmetics safety, environmental impacts as deforestation and social impacts as those resulting from unfair trade have intensified attention given to such topic. While sustainability impacts occur through all phases of the cosmetic product life cycle, selection of raw materials is deserving of greater attention as information on this topic remains scattered and diffuse. Formulating with alternative ingredients considered more sustainable can be quite challenging due to possible lack of performance, instability and aesthetic limitations normally associated with their use. This paper discusses the relation between sustainability and the cosmetics industry, the factors stimulating the developments on this field, the need to assess those and the available tools, alongside with the sustainability impacts produced during all the product life cycle. The analysis reveals cosmetics sustainability as a complex and multifaceted issue that cannot be evaluated considering single aspects, but using an integrated assessment about the environmental, social and economical dimensions and about the final product quality and performance.
Alkyl-branched fatty compounds are of interest for industrial products in the cosmetics and lubricant areas. In this review, clay-and zeolite-catalyzed isomerizations of unsaturated fatty compounds, especially of oleic acid, are discussed. While clay-catalyzed reactions give most complex mixtures of dimeric fatty acids and of monomeric so-called "isostearic acid", the zeolite-catalyzed process yields preferentially an isomeric mixture of isostearic acids having the methyl branch on the 8–14 positions of the alkyl chain. Synthetically useful additions of alkyl radicals can only be performed on o-unsaturated fatty compounds, whereas perfluoroalkyl iodides were added to fatty compounds with terminal as well as internal double bonds using electron transfer-initiated radical addition reactions. Electrophilic additions of alkyl carbe-nium ions generated by decomposition of alkyl chloroformates by ethylaluminum sesquichloride give well-defined alkyl-branched oleochemicals with good yields.
Although the chemistry named after Marcel Guerbet was developed over 100 yr ago, Guerbet alcohols, Guerbet acids, and derivatives
based upon them remain a topic of continued interest because of their (i) unique branching pattern, both in terms of size
of the branch group and purity of the compounds, (ii) oxidative stability, and (iii) liquidity of the products. This review
article is offered to demonstrate the diversity of chemistry possible using these materials and the large variety of applications
for which these compounds are useful.
Four triterpene acetates, alpha-amyrin acetate (1a), beta-amyrin acetate (2a), lupeol acetate (3a), and butyrospermol acetate (4a), and four triterpene cinnamates, alpha-amyrin cinnamate (1c), beta-amyrin cinnamate (2c), lupeol cinnamate (3c), and butyrospermol cinnamate (4c), were isolated from the kernel fat (n-hexane extract) of the shea tree (Vitellaria paradoxa; Sapotaceae). Upon evaluation of these eight triterpene esters for inhibitory activity against 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation (1 microg/ear) in mice, all of the compounds tested exhibited marked anti-inflammatory activity, with ID50 values in the range of 0.15-0.75 micromol/ear, and among which compound 3c showed the highest activity with ID(50) of 0.15 micromol/ear. Compound 3c (10 mg/kg) further exhibited anti-inflammatory activity on rat hind paw edema induced by carrageenan, with the percentage of inflammation at 1, 3, and 5 h of 35.4, 41.5, and 45.5%, respectively. The eight triterpene esters were then evaluated for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) in Raji cells as a primary screening test for inhibitors of tumor promoters. All the compounds showed moderate inhibitory effects. Furthermore, compound 3c exhibited inhibitory effect on skin tumor promotion in an in vivo two-stage carcinogenesis test using 7,12-dimethylbenz [a] anthracene (DMBA) as an initiator and TPA as a promoter. The biological activities of triterpene acetate and cinnamate esters, together with the exceptionally high levels of these triterpenes in shea fat, indicate that shea nuts and shea fat (shea butter) constitute a significant source of anti-inflammatory and anti-tumor promoting compounds.
The transesterification of vegetable oils with methanol as well as the main uses of the fatty acid methyl esters are reviewed. The general aspects of this process and the applicability of different types of catalysts (acids, alkaline metal hydroxides, alkoxides and carbonates, enzymes and non-ionic bases, such as amines, amidines, guanidines and triamino(imino)phosphoranes) are described. Special attention is given to guanidines, which can be easily heterogenized on organic polymers. However, the anchored catalysts show leaching problems. New strategies to obtain non-leaching guanidine-containing catalysts are proposed. Finally, several applications of fatty acid esters, obtained by transesterification of vegetable oils, are described.
Squalene is a triterpene that is an intermediate in the cholesterol biosynthesis pathway. It was so named because of its occurrence in shark liver oil, which contains large quantities and is considered its richest source. However, it is widely distributed in nature, with reasonable amounts found in olive oil, palm oil, wheat-germ oil, amaranth oil, and rice bran oil. Squalene, the main component of skin surface polyunsaturated lipids, shows some advantages for the skin as an emollient and antioxidant, and for hydration and its antitumor activities. It is also used as a material in topically applied vehicles such as lipid emulsions and nanostructured lipid carriers (NLCs). Substances related to squalene, including β-carotene, coenzyme Q10 (ubiquinone) and vitamins A, E, and K, are also included in this review article to introduce their benefits to skin physiology. We summarize investigations performed in previous reports from both in vitro and in vivo models.
Many studies have demonstrated beneficial health effects of topical antioxidant application; however, the underlying mechanisms are not well understood. To better understand the protective mechanism of oxogenous anti-oxidants, it is important to clarify the physiological distribution, activity and regulation of antioxidants. Also, the generation of ROS by the resident and transient microbial flora and their interaction with cutaneous antioxidants appears to be of relevance for the redox properties of skin. Our studies have demonstrated that alpha-tocopherol is, relative to the respective levels in the epidermis, the major antioxidant in the human SC, that alpha-tocopherol depletion is a very early and sensitive biomarker of environmentally induced oxidation and that a physiological mechanism exists to transport alpha-tocopherol to the skin surface via sebaceous gland secretion. Furthermore, there is conclusive evidence that the introduction of carbonyl groups into human SC keratins is inducible by oxidants and that the levels of protein oxidation increase towards outer SC layers. The demonstration of specific redox gradients within the human SC may contribute to a better understanding of the complex biochemical processes of keratinization and desquamation. Taken together, the presented data suggest that, under conditions of environmentally challenged skin or during prooxidative dermatological treatment, topical and/or systemic application of antioxidants could support physiological mechanisms to maintain or restore a healthy skin barrier. Growing experimental evidence should lead to the development of more powerful pharmaceutical and cosmetic strategies involving antioxidant formulations to prevent UV-induced carcinogenesis and photoaging as well as to modulate desquamatory skin disorders.
Self-diffusion coefficients and viscosities for the saturated hydrocarbons having six carbon atoms such as hexane, 2-methylpentane (2MP), 3-methylpentane (3MP), 2,2-dimethylbutane (22DMB), 2,3-dimethylbutane (23DMB), methylcyclopentane (McP) and cyclohexane (cH) were measured at various constant temperatures; obtained results were discussed in connection with their molar volumes, molecular structures and thermodynamic properties. The values of self-diffusion coefficients as the microscopic property were inversely proportional to those of viscosities as the macroscopic property. The order of their viscosities was almost same to those of their melting temperatures and enthalpies of fusion, which reflect the attractive interactions among their molecules. On the other hand, the order of the self-diffusion coefficients inversely related to the order of the melting temperatures and the enthalpies of the fusion. Namely, the compound having the larger attractive interaction mostly shows the less mobility in its liquid state, e.g., cyclohexane (cH), having the largest attractive interaction and the smallest molar volume exhibits an extremely large viscosity and small self-diffusion coefficient comparing with other hydrocarbons. However, a significant exception was 22DMB, being most close to a sphere: In spite of the smallest attractive interaction and the largest molar volume of 22DMB in the all samples, it has the thirdly larger viscosity and the thirdly smaller self-diffusion coefficient. Consequently, the dynamical properties such as self-diffusion and viscosity for the saturated hydrocarbons are determined not only by their attractive interactions but also by their molecular structures.
S ensory properties in skin care for-mulations are produced mainly by emollients, rheology modifiers, emulsifiers and humectants. Emollient esters are cos-metic ingredients that help maintain skin's softness and plasticity, form semi-occlusive films for moisturizing benefits, reduce the itching sensation often present in dry skin, and improve the appearance of the stratum corneum. As components of cosmetic formulations, emollient esters act mainly as moisturizers, plasticizers and tactile modifiers when applied to skin. 1, 2 In skin care emulsions, emollients are generally used at levels between 3–20% w/w, representing the second major ingredient after water. This use level var-ies depending upon several parameters including the oil phase composition, level of emulsifier blend, compatibility between ingredients, desired after feel, and the type, use level and solubility of UV filter in the ester (for sunscreens). Therefore, emol-lients play a major role in influencing the skin feel of formulations. 3 Based on their chemical structures, emollients can be categorized as esters, hydrocarbons, glycerides, ethers, fatty alcohols and silicone derivatives. When for-mulating cosmetics, the product developer's choice of emollient depends on several important factors such as chemical struc-ture, polarity, molecular weight, spreading attributes, viscosity, solubility, contact angle and surface tension. 4 The present study examines four known cosmetic emollient esters in vitro to assesses their physicochemical prop-KEY WORDS: sensory, esters, spreading, contact angle, surface tension, viscosity, dielectric constant, refractive index ABSTRACT: This study assesses the physicochemical properties of four known cosmetic emollient esters in vitro to predict their sensorial benefits and correlate their properties with in vivo sensory attributes. This evaluation serves as a guide to selecting specific emollient esters for various cosmetic applications and to predicting their sensory attributes. erties and correlate them with in vivo sensorial performance. The emollient esters investigated include: diisopropyl adipate a , isodecyl neopentanoate b , isocetyl stearate c and octyldodecyl stearoyl stearate d . These esters were selected for their broad range of molecular weights, with branched and/ or linear-branched alkyl carbon chains. Each has a distinct chemical structure, physicochemical characteristics and sensorial profiles. For all in vitro and in vivo assessments, the esters were tested as pure materials and not incorporated into finished formulations. Characteristics measured include spread-ing values on an artificial membrane, contact angle, surface tension, dielectric constant, refractive index and viscosity. Following in vitro assessments, an in vivo sensory panel test was conducted to investigate the perceived sensory attributes of the same emollient esters after application to skin. This study demonstrates that the physicochemical properties of ester molecules can be cor-related with their distinct sensory profiles.
Eight liquid emollients (mineral oil, sunflower oil, squalane, decyl-oleate, isopropyl-myristate, octyldodecanol, dimethicone, and cyclomethicone) were characterized by instrumental and sensory methods and evaluated to determine the relationship between sensory and instrumental measures. Sensory analysis was carried out by a panel of 14 assessors, who evaluated the following attributes: difficulty of spreading, gloss, residue, stickiness, slipperiness, softness, and oiliness. The physicochemical properties measured were spreadability (at 1½ and 1 min), viscosity, and superficial tension. Data collected were statistically analysed by analysis of variance (ANOVA), principal component analysis (PCA), and linear partial least squares regression analysis (PLS). In consideration of their physicochemical characteristics, the studied emollients were sorted into three groups, in which the silicones distinctly separate from the rest. Sensory characteristics enabled the discrimination of four groups of emollients where, besides the two silicones, isopropyl myristate was also differentiated. PLS revealed that emollient sensory attributes could be well predicted by instrumental measurements.
Abstract Various aspects of soft paraffins, with the main emphasis on their rheological properties, are considered in a review of 119 references. Rheological test methods currently used are critically appraised in sections on penetrometry, continuous shear viscometry, oscillatory testing and creep analysis. The chemical nature, microscopic structure, miscellaneous methods of standardisation, formulation and work softening of petrolatums are reviewed. The textural properties of soft paraffins are discussed; a master curve of the rheological conditions operative during spreading on the skin is presented.
A wide range of fatty acid esters can be synthesised by esterification and transesterification reactions catalysed by lipases in non-aqueous systems. As well as modifications to the natural substrate triacylglycerol, many other commercially important substances can be produced using this enzyme technology, as lipases have been shown to have broad substrate specificities and can thus catalyse conversions with many other non-glycerol based compounds. In mild reaction conditions, emollient esters for use in the personal care industry can be made with excellent quality.
Development of economical processes was necessary to commercialise this technology for the manufacture of cosmetic ingredients. Enzymatic production methods had to be established which could compete against standard established chemical synthetic methods. Now relatively simple esters are being produced enzymatically. Extensive purification procedures to clean up products after high temperature reaction steps are not required. Product quality and specifications, such as the acid and hydroxy values of commercial ester products, could be improved. Examples of products manufactured with better purity and yields in economical and ecologically friendly processes are decyl oleate, cetyl ricinoleate, myristyl myristate and decyl cocoate.
Active ingredients have been around in cosmetics for a long time but have they really resulted in active cosmetic products? In order to achieve this, the right ingredient needs to be delivered to the right location at the right concentration for the correct period of time and the extent (and therefore the concentration) of this delivery depends on the formulation.
From a rather theoretical approach based on the polarity of the active ingredient, the stratum corneum and the oil phase, the relative polarity index was established that enables the selection of a suitable emollient for ensuring skin penetration of the active ingredient. Practical examples subsequently show the validity of this approach that demonstrates that one can regulate the delivery of an active molecule (and therefore the efficacy of a cosmetic formulation) by selection and control of the emollient system. Cosmetic formulations are generally quite complex mixtures and subsequent experiments using different emulsifier systems indicated that this component of a cosmetic formulation could also have an impact on steering the active ingredient to the right layer of the skin, although it is too early to be able to derive general rules from this.
A review of the literature on wool wax hydrocarbons reveals that the hydrocarbons represent about 0.5% of wool wax and that
they consist of a large number of normal and branched homologs. This, in turn, shows a structural similarity between the hydrocarbons
and the wool wax acids or wool wax aliphatic alcohols: all three materials contain normal, iso and anteiso series. The wool
wax hydrocarbons also contain highly branched alkanes as well as cycloalkanes.
Lanolin, which is extensively used in pharmaceuticals and cosmetics, is generally considered to consist of a mixture of naturally
formed esters derived from higher alcohols and higher fatty acids. This paper encompasses the chemical description of lanolin;
the composition of its esters, acids, and alcohols; the chemical and physical modifications of lanolin; the refining of lanolin;
and some of its applications in pharmaceutical and cosmetic formulations. Some new developments in lanolin chemistry will
also be high-lighted.
A lack of reliability in the usual determinations of fatty acids and fatty alcohols of jojoba wax prompted us to propose an
original method of hydrolysis and extraction, making it possible to better determine the composition of fatty acids and alcohols
of the wax. High-performance liquid chromatography fractionation of the wax allowed isolation of four main classes of esters
(which differed by their partition number). The detailed study of these ester classes emphasized the way acids and alcohols
are connected, and fourteen distinct esters were thus identified. Some triacylglycerols, free fatty alcohols and other minor
components of jojoba wax were found and quantitated. Seven sterols were identified, four for the first time.
Wool wax alcohols consist of aliphatic monoalcohols and alkane 1,2 diols, cholesterol, triterpene alcohols, and small amounts
of hydrocarbons and autoxidation products. The monoalcohols and the diols consist of normal, iso and anteiso series. The average
composition of the wool wax alcohols is based on data which were published during the past 25 years.
Wool wax acids consist predominantly of alkanoic,α-hydroxy andω-hydroxy acids. Each group contains normal, iso, and anteiso series of various chain length. Practically all the acids are
saturated. The average weight-percent of the various series is based on recently published results.
Olive oil deodorization distillate contains squalene in a concentration range of 10 to 30 wt%. A process for its recovery
by supercritical carbon dioxide extraction is described. The process consists mainly of converting the free fatty acids and
the methyl and ethyl esters normally occurring in this by-product into their corresponding triglycerides. The latter are then
extracted with supercritical carbon dioxide to provide a highly enriched squalene fraction. The process has been carried out
on a pilot-plant scale with a column operating in the contercurrent mode. The relationship between the experimental conditions
and squalene purity and yield has been studied. Analytical methods were used for the determination of squalene and other components
in the fractions. By use of this process, squalene can be recovered in high purity and yields of about 90%.
Lipids are a major component of food and important structural and functional constituents of cells in biological systems. However, this diverse group of substances is prone to oxidation through various pathways. Their oxidative stability depends on a number of intrinsic and extrinsic factors, including the unsaturation of their fatty acids, composition of minor components, environment conditions, delivery techniques and use of antioxidants, among others. Lipid oxidation has detrimental effects on both food quality and human health, and efforts must be made to minimize oxidation and improve oxidative stability of lipid products. Antioxidant strategy has been successfully employed in the food industry for quality preservation of the food products and in the medicinal industry for risk reduction of numerous oxidative stress-mediated diseases. This tutorial review will provide important knowledge about lipid oxidation, including the mechanism and factors involved in oxidation, as well as strategies for improving oxidative stability of lipids.
Synopsis
It has been recognized that the vehicle in which a permeant is applied to the skin has a distinctive effect on the dermal and transdermal delivery of active ingredients. The cutaneous and percutaneous absorptions can be enhanced, e.g. by an increase in thermodynamic activity, supersaturation and penetration modifiers. Furthermore, dermal and transdermal delivery can be influenced by the interactions that may occur between the vehicle and the skin on the one hand, and interactions between the active ingredient and the skin on the other hand. Emulsions are widely used as cosmetic and pharmaceutical formulations because of their excellent solubilizing capacities for lipophilic and hydrophilic active ingredients and application acceptability. This review focuses, in particular, on the effect of emulsions on the dermal and transdermal delivery of active ingredients. It is shown that the type of emulsion (w/o vs. o/w emulsion), the droplet size, the emollient, the emulsifier as well as the surfactant organization (micelles, lyotropic liquid crystals) in the emulsion may affect the cutaneous and percutaneous absorption. Examples substantiate the fact that emulsion constituents such as emollients and emulsifiers should be selected carefully for optimal efficiency of the formulation. Moreover, to understand the influence of emulsion on dermal and transdermal delivery, the physicochemical properties of the formulation after application are considered.
Skin surface lipids and lipids from open and closed comedones in acne patients were analysed by thin layer chromatography. The results showed that these lipids were enriched in polar lipids, as compared with the skin surface lipids obtained from controls without acne. In both open and closed comedones, these polar lipids appeared to be derived mainly from the oxidation of squalene, which is in agreement with our previous in vitro results.
We suggest that squalene oxidation is the link between comedogenesis and bacterial colonization, and based on this, we propose a hypothesis of the pathogenesis of acne.
An in vitro study of the oxidation of squalene, and a description of factors acting on this transformation are presented. Thin layer chromatography was used to quantify the products generated by different oxidation processes. The results clearly show that squalene is a highly effective oxygen-scavenging agent. Its oxidation may first induce comedogenesis and, as a secondary event, cause a large reduction in oxygen tension in the human pilo-sebaceous duct. Porphyrins were confirmed to be highly efficient catalytic factors in the squalene oxidation process. The relationships between comedogenesis, bacterial colonization, and the role of sebum in the pathogenesis of acne are discussed in the light of these findings.
The comedogenicity of UVA-irradiated and non-irradiated substances (squalene, oleic acid, tetradecane, isopropyl myristate, squalane and liquid paraffin) was evaluated by surface microscopy and histological examination after treating the ventral skin of rabbit ears with these substances. The lipid peroxide levels of these substances were also measured. Squalene itself was scarcely comedogenic but squalene peroxides were highly comedogenic. Both oleic acid and its peroxides were able to induce fairly large comedones and there was a good correlation between the lipid peroxide levels and the size of the comedones. The specimens biopsied from these comedones showed marked hyperplasia and hyperkeratosis of the epithelium in the follicular infundibulum and marked proliferation of the sebaceous glands.
Although free fatty acids might play a role in the pathogenesis of acne, it is proposed that squalene and free fatty acids in sebum may be less comedogenic than their peroxides.
Summary Moisturizers are used daily by many people to alleviate symptoms of dry skin. All of them contain lipids. It has been suggested that topically applied lipids may interfere with the structure and function of the permeability barrier. The influence of a single application of nine different lipids on normal skin and skin irritated by sodium lauryl sulphate (SLS) was studied in 21 healthy subjects. Parameters assessed were visible signs of irritation, and objectively measured cutaneous blood flow and transepidermal water loss (TEWL). The substances tested were hydrocortisone, petrolatum, fish oil, borage oil, sunflower seed oil, canola oil, shea butter, and fractions of unsaponifiable lipids from canola oil and shea butter. Water was included as a control.
On normal skin, no significant differences in the effects of the test substances were found, whereas significant differences were observed when they were applied to SLS-irritated skin. The visible signs of SLS-induced irritation were significantly less pronounced after treatment with the sterol-enriched fraction from canola oil than after treatment with water. This fraction, and hydrocortisone, reduced cutaneous blood flow. Furthermore, application of hydrocortisone, canola oil, and its sterol-enriched fraction, resulted in significantly lower TEWL than with water. The other lipids had no effect on the degree of irritation.
In conclusion, lipids commonly used in moisturizers may reduce skin reactions to irritants. Previous studies have shown that, in barrier perturbed skin, the synthesis of sterols is increased. The observed effects of canola oil and its fraction of unsaponifiable lipids on SLS-induced irritation suggest the possibility that they assisted the skin in supplying the damaged barrier with adequate lipids.
Skin is a highly metabolic tissue which possesses the largest surface area in the body and serves as the protective layer for internal organs [1]. Skin is also a major candidate and target of oxidative stress. It is designed to give both physical and biochemical protection, and is equipped with a large number of defense mechanisms. The skin tissue is exposed to a variety of damaging species which originate in the outer environment, in the skin itself, and in various endogenous sources [2, 3]. The structure of skin is quite complex being composed of several layers, each of which plays a specific role and carries out different functions [4]. Each layer is equipped with its own arsenal of defense molecules, and the various systems differ from each other based on the layer's susceptibility to oxidative stress and its function. It is generally agreed that one of the major and important contributions to skin aging, skin disorders and skin diseases results from reactive oxygen species (ROS) [1, 5]. Due to the high occurrence of potential biological targets for oxidative damage, skin is very susceptible to such reactions. For example, skin is rich in lipids, proteins, and DNA, all of which are extremely sensitive to the oxidation process [6-8]. Elucidation of the mechanisms involved in skin oxidation and the examination of the defense systems may contribute to the understanding of skin aging and of the mechanisms involved in the various pathological processes of skin. This review addresses the antioxidant defense mechanism of the skin, the role it plays during the aging process, and the role skin has following exposure to oxidative stresses.
The comedogenicity of squalene peroxides was examined on the rabbit ear skin after topical application of squalene-monohydroperoxide (Sq-OOH), the initial product when squalene was irradiated with UV-A. Since comedogenic products from UV-irradiated squalene were extracted with methanol solution, we isolated Sq-OOH by reverse-phased HPLC with a methanol mobile phase solvent. The degree of comedogenic reaction induced by Sq-OOH was higher than that of well-known comedogenic cosmetic ingredients. Unlike two other mono-peroxides, tert-butyl hydroperoxide and cumene-mono-hydroperoxide, Sq-OOH induced comedo-formation in the rabbit ear skin. However, the comedogenicity of reduced Sq-OOH, squalene-hydroxide (Sq-OH) and squalene itself was lower than that of Sq-OOH. These results indicate that Sq-OOH is a potent comedogenic mono-hydroperoxide chemical to rabbit skin.
Concepts of HLB, HLB temperature and HLB number. In: Emulsions and solubilization
- K Shinoda
- S Friberg
Phase poperties of emulsions: PIT and HLB
- K Shinoda
- H Kunieda
Novel methods for emollient characterisation
- K J Hughes
- V F Lvovich
- J Woo
- B Moran
- A Suares
- Mht Truong
- KJ Hughes
Fractionated products: a brief survey of the application of fractions of edible oils and fats
- F B Padley
- FB Padley
Identification of topical excipients with high performance spreadability. Poster, 5th world meeting on pharmaceutics
- C Bruns
- R H Müller
- D Prinz
- G Kutz
Production and refining of vegetable oils The lipid handbook with CD-ROM
- Aj Dijkstra
- Jc Segers