A lot of research correlates sensory perception with physicochemical properties of cosmetic oils and esters, but John Woodruff finds a lot of natural oils now available also have exciting stories to tell
The INCI Dictionary, 12th Edition 2008, defines oils and fats as the glyceryl esters of fatty acids normally found in animal and plant tissues and lists these plus those which have been hydrogenated to reduce or eliminate unsaturation under the heading of fats and oils. Naturally occurring fats and oils can be hydrolysed to yield glycerin and mixtures of fatty acids. Alternately, isolated and purified fatty acids can be esterified with glycerin to yield mono-, di- and triglycerides. The last are relatively pure fats which differ only slightly from the fats and oils found in nature. Also of cosmetic interest are synthetically prepared esters of glycerin and fatty acids.
An article on the subject of cosmetic oils appeared in SPC May 2007 (p30-32 and www.cosmeticsbusiness.com). The meaning of the physical and chemical attributes that may be found in specifications of oils was explained and tables produced by various suppliers to assist the formulator in making a choice of oil for specific applications were described. However, finding tables that give physical and chemical constants for natural oils is not easy. Individual suppliers may list the properties of their specialities but seldom are extensive listings found. The suspicion is that the more exotic oils are included in cosmetic products at the behest of the marketing department that cannot resist a good story, and the formulator is left with the task of combining these with carrier oils of more mundane origin but which are stable, relatively odourless and that do not contravene the overall product concept.
Arguably the principal function of oil in a cosmetic product is as an emollient, although emolliency is a somewhat vague term relating to the user’s perception of the spreading characteristics and tactile properties such as skin smoothness, elasticity and lubrication. Some years ago R Goldemburg proposed a Skin Feel Index based on sensorial evaluation for quantifying emollient properties of 85 cosmetic emollients.[1] It was found that molecular weight was not relevant to skin feel but oiliness was. Polar groups gave significantly negative effects, while a degree of unsaturation or chain branching was usually beneficial. Finally the authors reported that the isopropyl esters of most fatty acids were outstanding as emollients.
The difficulty of using such a large number of subjects led Hans Brand to measure the lubricity and spreadability of various emollients. Brand defined and measured application emolliency and residual emolliency and grouped emollients into those that were principally protective, provided a fatting effect, or were dry and astringent.[2]
There have been various other studies linking sensory perception with the physicochemical properties of the materials under consideration. M E Parente characterised eight liquid emollients - mineral oil, sunflower oil, squalane, decyl oleate, isopropyl myristate, octyldodecanol, dimethicone and cyclomethicone - by instrumental and sensory methods and characterised them by instrumental and sensory methods.[3] J Wiechers evaluated the attributes of difficulty of spreading, of gloss, residual stickiness, slipperiness, softness and oiliness and correlated this with the Relative Polarity Index (RPI). The RPI compares the polarity of an active ingredient with that of the stratum corneum and the emollient components of cosmetic formulations. Using this method Wiechers was able to optimise the delivery of active ingredients from a cosmetic product into the stratum corneum.[4]
Much research has been done on correlating sensory perception with physicochemical properties of cosmetic oils and esters. Jan Dekker publishes an overview of oils and fats with brief details of how they are obtained and treated to make them fit for purpose. Thus steam distillation is a deodorising step that removes free fatty acids, peroxides and degradation products and organo-chlorine pesticides but it also removes sterols and tocopherols. These latter materials may be extracted from the distillate and returned to the oil as natural antioxidants. The brochure includes a chart of the more popular natural oils with ratings for penetration rate, spreadability, dry feel and fatty feel. Jan Dekker also publishes a chart showing the iodine value and fatty acid profile of an extensive list of natural oils. The higher the iodine value the more unsaturated fatty acids are present and the more prone the oil is to oxidation. However, high iodine values also increase spreadability and improve penetration into the stratum corneum.
Until recently the benefits of using oils in cosmetics has been largely related to sensory perception and improving skin moisturisation. However, most natural oils have been used by indigenous populations as foodstuffs and beauty aids, and research into these uses reveals some interesting results. A good example is shea butter, which is well known to consumers as a highly moisturising vegetable oil with good skin feel. It is also thought to have skin healing and skin protective attributes, primarily from its triterpene esters, which have anti-inflammatory properties and are able to stimulate the proliferation of fibroblasts, which are important in skin regeneration.
ADDED BENEFITS
To add physiological and monetary value to natural oils various producers have enhanced their properties by extracting or concentrating the more active principals. Thus AAK supplies Lipex 205, a modified shea butter in liquid form with enhanced bio-active unsaponifiables content. The fatty acid composition of liquid shea butter is predominantly oleic and stearic acid plus
8 - 10% linoleic acid. An advantage of Lipex 205 is that it does not crystallise when used in lipsticks, body butters and other high wax content products.
Signaline from ISP-Vincience is a patented active ingredient composed mainly of 1,2-diacylglycerol (1,2-DAG) obtained from Olea europaea (olive) oil by enzyme hydrolysis with about 10% of fatty alcohols extracted from Simmondsia chinensis (jojoba) wax. Efficacy studies show that Signaline increases calcium signalling, which in turn activates various calcium-dependent enzymes and improves cell functioning and epidermal differentiation. Collagen, filaggrin, fibronectin and keratin synthesis is increased, dermal fibroblast production enhanced and skin properties of firmness, elasticity and reduction in wrinkles greatly improved.
Olive oil is a favourite starting point for cosmetic ingredients. Fancor has isolated the unsaponifiable fraction and offers it as Silk Olea Oil. The unsaponifiable fraction of natural oils is usually the source of its active ingredients and these are often supplied in more concentrated form to enhance their properties. An example is ABS Pomegranate Sterols [INCI: Punica granatum (pomegranate) fruit sterols] from Active Concepts, said to improve skin hydration and to enhance its barrier function. A combination of caprylic/capric/succinic triglyceride with Sesamum indicum (sesame) oil, Triticum vulgare germ oil and tocopheryl acetate is offered by Atrium for protecting human skin from dehydration and inflammation.
The importance of omega-3 & 6
Linoleic acid is an omega-6 fatty acid and an essential building block of ceramides and signalling substances in the skin. Linoleic and alpha-linolenic (omega-3) acids are called essential fatty acids; they cannot be synthesised by the body and consequently need to be supplied from food. But lipids can penetrate the upper layers of skin and topical application makes it possible to directly target skin lipid layers and improve skin quality. The omega-6 linoleic acid is the more important and is found mainly within the ceramides and cholesterol that help maintain the epidermal water barrier. Topical application of linoleic acid helps restore the levels of this fatty acid in dry skin or skin damaged by surfactants, thereby reducing transepidermal water loss.
The importance of omega-3 fatty acids for skin is their anti-inflammatory and photo-protective properties. Current dietary recommendations for omega fatty acids usually suggest a ratio close to 1:2 (omega-3: omega-6) for adult nutrition. However, in healthy skin the natural ratio is 1:7 and AAK has produced three oil blends that provide omega-3 and omega-6 fatty acids at this optimum ratio. Lipex Omega 3/6 has essential fatty acids derived primarily from the seeds of Camelina sativa (gold of pleasure). For Lipex Omega EPO, the main source of essential fatty acids is Oenothera biennis (evening primrose) oil, rich in both linoleic acid and gamma-linolenic acid. Finally, Passiflora incarnata (passionflower) oil is used as a source for the essential fatty acids in Lipex Omega Passiflora. An advantage of these oils is their oxidative stability compared to the natural oil before enhancement. AAK recommends a use level of 5% or more in the final formulation to provide a beneficial effect on stressed skin conditions such as atopic dermatitis or chronic dry skin conditions.
DSM is well known for its vitamins and nutritional supplements and cosmetic actives. It supplies omega-6 oils under the name of Ropufa 10, obtained from evening primrose, and Ropufa 25 from Borago officinalis (borage) seed oil. Its brochure describes polyunsaturated fatty acids as being as essential as vitamins, mineral salts and proteins. They are basic substances from which not only skin lipids and cell membranes but also hormones and prostaglandins are synthesised.
There are many oils in common use as carriers and for their skin feel. A recent introduction is Prunus domestica seed extract supplied as virgin prunus oil cold pressed from the seed kernel of the Ente plum tree. It is described by Laboratoires Expanscience as having a pleasant natural fragrance and on application it spreads well with rapid penetration properties, imparting a smooth, dry skin feel. Its fatty acid composition is similar to that of other Prunus species, being approximately 70% oleic acid and 20% linoleic acid. It has a high content of natural tocopherols, ensuring good oxidative stability.
An exotic ingredient with a good story has always fascinated the cosmetics industry and oils of natural origin often provide both. Carapa guaianensis (andiroba) seed oil is from the Amazon basin and has long been used by the Wayapi and Palikur Indians, who apply it to the body to repel insects and for its anti-inflammatory and skin soothing properties. The ripe fruit falls into the river and is carried to the Amazon delta where the local population collects it from the sand banks. The oil is obtained by pressing the dried fruit and the first pressing is decanted, filtered and stored under nitrogen. Laboratoires Expanscience refines this oil to remove free acidity and enriches it with natural tocopherol to improve its oxidative stability.
Nuts, fruits & butters
Also from the Amazon basin and obtainable from Laboratoires Expanscience and
others, Bertholletia excelsa (Brazil) nut oil is a popular cooking oil in the area and is also used for soap making in Peru. The trees grow up to 30m in height and the fruit, which contains between 12 and 20 seeds closely packed together, can weigh up to 2.5kg. Brazil nuts are probably the best known source of oil from the Amazon area; they are a three sided nut with white meat that consists of 70% fat or oil and 17% protein. Brazil nuts are a substantial source of selenium, an important antioxidant and one single Brazil nut exceeds the US Recommended Daily Allowance of selenium. The proteins found in Brazil nuts are very high in sulphur-containing amino acids like cysteine (8%) and methionine (18%) and are also extremely rich in glutamine, glutamic acid and arginine.
Chemyunion publishes an extensive document about Brazil nuts, detailing their collection and use by native tribes and the properties of the oil. Caryocar brasiliense fruit oil is described by Chemyunion as an oil obtained from the fruit of the pequi tree that grows in Central and South America. It contains about 60% edible oil rich in vitamin A and proteins and is an important element in food and nutrition of the indigenous population and is also used locally to produce soap. Analysis of the butter extracted from its pulp shows a composition rich in carbohydrates, trace elements and fatty acids as well as a steroid fraction, amino acids and volatile compounds.
According to Gattefossé, Sacha inchi oil is a rich and natural legacy from the ancient civilizations of Peru that has been carefully guarded until recent times by indigenous communities in the Peruvian rain forest. It is a native oleaginous plant whose seeds have a high content of unsaturated fatty acids such as omega 3, 6 & 9.
Calophyllum tacamahaca (tamanu) oil is obtained from the seeds of wild Calophyllum inophyllum that grows along the southern part of the east coast of Madagascar. The Concentrated Aloe Corporation (CAC) supplies it as pure virgin oil containing approximately 92% neutral lipids, 6.4% glycolipids and 1.6% phospholipids. Trials initiated by CAC demonstrate scar healing properties and improvements in skin firmness, elasticity and smoothness. It also has antibacterial properties against a number of gram negative and gram positive bacteria, including an MIC of 3mg/ml against Propionibacterium acnes.
The Indian sub-continent is also a rich source of natural ingredients including Mangifera indica (mango) seed butter. A butter is an oil with a titre between 20°C and 40.5°C and those above 40.5°C are termed fats. Titre is defined as the solidification point of a melted oil, fat or wax. Waxes are esters of fatty acids with fatty alcohols. Jan Dekker provides a very descriptive leaflet about mango seed butter and its ancient mythology.
Other butters include Theobroma cacoa (cocoa) seed butter, Butyrospermum parkii (shea) butter and Persea gratissima (avocado) fruit butter. These are refined natural extracts but also available from Lipo are partially hydrogenated vegetable oils that increase their viscosity to a buttery consistency. Zenitech provides numerous butters including raspberry, cranberry, avocado, carnauba, lemon, lime, watermelon and blackcurrant. They are derived from high purity cold-pressed vegetable oils and beeswax and offer exceptional skin feel and good barrier properties.
Thickening oils with natural ingredients is of interest to many formulators. A recent introduction by Gattefossé is Compritol 888; a mixture of mono-, di- and triglycerides of behenic acid. When incorporated in the oil phase at use levels of 1% to 3%, Compritol 888 increases the stability and viscosity of emulsions, at the same time improving the softness and play time of the creams and it will not soap or whiten upon application to the skin. It can also be used to gel oils; between 4 - 8% will create an anhydrous gel with most vegetable oils, 10 - 20% will gel the majority of esters and about 15% is necessary to gel mineral oils and silicone fluids.
Finally, a major problem with vegetable oils is oxidation and rancidity. Conventional antioxidants are not wanted by those seeking organic or natural approval so natural ones are required. Tocopherols are the most widely known and occur naturally in the majority of natural oils. There are four homologues: alpha-, beta-, gamma- and delta-. Cognis supplies various mixtures under its Controx and Covi-ox trade names.
Tocmix L70 from Jan Dekker is a concentrated mixture of natural tocopherols, high in gamma- and delta that have the highest antioxidant efficacy and low in alpha- which can promote oxidation. Jan Dekker also produces antioxidants based on Rosmarinus officinalis and mixtures of natural antioxidants include Phytox LT, a mixture of tocopherol, ascorbyl palmitate and lecithin. Danox R-3204 from ICSC is an oil solution of natural antioxidants extracted from dry leaves of Rosmarinus officinalis. By applying modern techniques of extraction, the characteristic odour and flavour have been removed and between 500ppm and 1000ppm, based on the weight of the vegetable oil content, is recommended.
