Creative Developments (Cosmetics) Limited

Emollients 1999

 

The use of the term emollient did not appear in cosmetic textbooks until about 1960. It was used much earlier in pharmacy; Pharmaceutical Formulas, 1934 [ref 1] describes the addition of 21/2 lb of bran to the water to make an emollient bath. Glycerin and honey with rose water was suggested for an emollient lotion and petrolatum with beeswax plus camphor and eucalyptus oils were recommended for an emollient ointment. Pharmaceutical and Cosmetic Preparations for Topical Administration, 1969, states that water is the only substance having a direct emollient effect (on the skin) of any significance [ref 2]. However the authors admit that if a broader view is taken the term can be expanded to include the control of hydration and dehydration of the horny layer and the lubricating properties of the application. This feature will take the broader view.

 

Whatever term was used, until relatively recently skin hydration was achieved by the application of an occlusive film of petrolatum with mineral oil and paraffin wax to the skin. This provided slip and lubrication and prevented trans-epidermal water loss (TEWL). It is an effective system and still forms the basis for many popular products, both cosmetic and pharmaceutical. Occlusive films are best applied either as an anhydrous preparation or a w/o emulsion. Olivem 900 from B&T Srl is sorbitan olivate and may be used to prepare anhydrous systems and w/o emulsions. If mixed with oils and esters it forms a gel that can vary from firm to pourable, depending on the lipid and its polarity. Trials were undertaken using 30% Olivem 900 to 70% lipid and in the majority of cases the gels were stable, easy to spread and with a pleasant emollient feel. Altering the ratio alters viscosity and the gelling action is maintained down to 10% Olivem 900 to 90% lipid. It is also possible to incorporate powders and pigments into the gels and in many cases a higher loading of solids is possible than for the lipid alone. The anhydrous gels can be mixed with water to form w/o emulsions and some interesting formulation ideas are possible.

 

Olive oil is the basis for Waxolive and Beurrolive, two hydrogenated olive oil products from EX.A International and olive wax, olive butter and a number of other naturally derived waxes are supplied by Ceratec S.A.R.L. Every year sees the introduction of new vegetable oils. Two oils from A&E Connock are each a good source of g-linolenic acid and stearidonic acid; ingredients that are thought to be useful for treating inflamed skin. Echium seed oil typically contains 11% g-linolenic acid and 14% stearidonic acid and Shikonin seed oil from lithospermum erythrorohizon has 13.3% g-linolenic acid and 12.5% stearidonic acid.  A third oil from A&E Connock is Artemisia sphaerocephala seed oil, which is cold pressed from natural wild plants growing in the Chinese desert. It has a high natural tocopherol content and also contains b-carotene.

 

The number of w/o emulsifiers available has increased substantially over the past decade and the result is lighter more elegant w/o emulsions are replacing those that rely on high oil and wax content to render them stable. Many w/o emulsifiers are lanolin-based or are low HLB sorbitan or glyceryl esters or alkoxylated alcohols and these ingredients are often combined in emulsifying bases like the well-known Dehymuls series from Cognis and the Protegin series from Goldschmidt. For the formulator looking for alternatives the author can report good results in his own laboratory when working with Arlacel P135 (PEG-30 Dipolyhydroxystearate) from Uniqema, from Montanov WO18 (isostearyl glucoside with isostearyl alcohol) from Seppic and a with a mixture of methoxy PEG 22 dodecylglycol copolymer with PEG 45 dodecylglycol copolymer from A&E Connock. All three systems can be used to form w/o, w/Si and w/o/w emulsions covering a wide range of viscosities. Like many emollients, they each have good dispersing properties for pigments and microfine oxides.

 

The oiliness of w/o emulsions is a drawback and this may be reduced by the addition of suitable esters, which reduce the film viscosity, improve spreading and enhance penetration. A new generation of esters are described as dry emollients. Dicaprylyl carbonate from Cognis is a good example. It has high spreading properties and leaves a dry, velvety feel to the skin. Cognis developed the Cascade System of emollient choice whereby a mixture of light, medium and heavy viscosity lipids are combined to provide the desired sensory profile throughout the application of the finished composition. Dicaprylyl carbonate is recommended as a fast spreading component. It also forms small droplets in emulsions, which is a sign of easy emulsification and long-term emulsion stability. A useful application of caprylyl carbonate is in sun protection products based on ethylhexyl methoxycinnamate. This sunscreen is slow spreading but by adding cocoglycerides and caprylyl carbonate the overall effect is one of smoothness on application and the active is evenly spread on the skin surface as an emollient film.

 

Esters that have good spreading properties are often useful for pigment dispersing and also for improving sun products incorporating microfine oxides. The main criterion for high SPF with minimum whitening is good dispersion and the prevention of subsequent agglomeration. Caprylyl carbonate is said to provide both properties. The C8 alkyl chain of the caprylyl molecule ensures compatibility with a wide range of mineral and vegetable oils, esters and triglycerides. Silsoft 034, OSi Specialties, is caprylyl methicone where the silicone is trisiloxane and this material improves the smoothness and lightness of oils and reduces tackiness without affecting emollient characteristics.

 

Silicone elastomers from Dow Corning are also classified as dry emollients and their effect is described as silky/powdery when incorporated into skin creams, sun creams and cream-to-powder foundation compositions. Data published by the supplier shows sensory evaluation results when the elastomer replaced cyclopentasiloxane in a number of formulations. The Dow Corning silicone elastomers are dimethicone crosspolymers with either cyclomethicone or divinyldimethicone. Alkyl methicones also claim to be dry emollients and those based on higher alkyl chain are wax-like and may be used to add viscosity to emulsions while as little as 0.10% of the lower alkyl chain variants may be used to lower surface tension and thus enhance the spreading power of many esters.

 

Low viscosity hydrocarbons are becoming increasingly popular alternative emollients to silicones and esters, Hydrogenated polybutene has a branched-chain aliphatic hydrocarbon structure and is described as non-comedogenic, non-irritating to skin and eyes and is stable over a wide pH range. It is clear, colourless and odourless, is resistant to oxidation and remains unaffected by normal processing temperatures. It leaves a non-greasy emollient film on the skin and may be used to formulate water-resistant sunscreens as well as improving the skin feel of emulsions and makeup.. Various grades with differing viscosity are available as the Panalene range from Amoco Chemical Co. and as Prisorine 3758 from Uniqema. Polydecenes are fully hydrogenated oligomers of 1-decene and are non-volatile, non-toxic, odourless and colourless. They have many similar properties and applications to hydrogenated polybutenes and are available under the Silkflo name from Lipo Chemicals, as PurSyn from Mobil and Nexbase from Neste of Finland.

 

Another approach to providing emolliency does not rely on the prevention of TEWL but instead it improves hydration by the application of proven moisturisers. There are many materials with such claims; glycerin is the simplest; collagen, hyaluronic acid, chitosan and other protein-based materials combine good water-binding capacity with skin substantivity. Reproducing the skin’s natural moisturising factor (NMF) with mixtures of sodium PCa, urea, amino acids and sodium lactate is effective. Wheat and other vegetable proteins, trehalose and other sugars and Aloe Barbadensis (Aloe Vera Gel) are all much used. Glyceryl polymethacrylate as Lubragel from United-Guardian, has been with us in various grades for more than a decade but these clear water-soluble materials still provide exceptional moisturising benefits in a wide range of applications. A silicone-based gel is Gel Base BSM5 from Brooks Industries. This is a combination of dimethicone, cyclomethicone and phenyltrimethicone; it is soluble in silicone fluids, compatible with isododecane and dispersible in mineral oil, butylene glycol and ethylhexyl palmitate. It is said to deposit a water-resistant emollient film on the skin and to also improve facial appearance by an optical diffusing effect. Gel Base BSM5 is particularly recommended for makeup and sun protection products.

 

Adding emollients via a shower would seem a contradiction but cream body washes are the fastest growing segment of the bathroom toiletries market [ref 3]. There are various approaches to adding emolliency to such products including the addition of silicone compounds and refatting materials and incorporating an emulsion with moisturising properties, which allows 2-in-1 claims. Lamesoft PO 65 from Cognis is a mixture of glyceryl oleate and coco-glucoside that when added at 5% to a shower gel is said to significantly improve skin softness, suppleness and elasticity without loss of foam. Mackanate DC-50 from the McIntyre Group is disodium dimethicone copolyol sulfosuccinate and is said to add both foam stability and emolliency and Antil B 8832 from Goldschmidt AG is a dimethicone copolyol that adds slip and skin feel to body wash products.

 

Many cream body wash formulations include the addition of an oil phase to create a moisturising lotion within a foaming product. Uniqema has advanced the use of Arlatone Duo for such products. This proprietary composition forms a liquid crystal structure in water and itself has a moisturising and emollient effect that can be enhanced by the addition of further lipids. Those of medium polarity are recommended and Helianthus annuus (hybrid sunflower) seed oil has both a good skin feel and improves product stability. Additional foaming aids may also be added and product viscosity can be increased using Xanthan gum. Patent USP 6,066,607describes the moisturising phase of a cream body wash as follows “A method of cleaning and moisturizing the skin wherein the skin conditioner ingredient within the moisturizing phase comprises ingredients selected from the group consisting of esters of fatty acids, glycerin esters, epidermal and sebaceous hydrocarbons, lanolin, mineral oil, silicone oil, silicone gum, vegetable oil, petrolatum, vegetable oil adduct, cationic polymer and mixtures and derivatives thereof” The illustrative formula shows typical ingredients and their range as a % of the composition encompassed by the patent.

 

Water

55.0%w/w

60.0 w/w

Cocoamphoacetate/Cocoamphodiacetate

4.00

8.00

Sodium Laureth-3 Sulfate

10.00

15.00

Alkylpolysaccharide

0

3.00

Coconut MEA

2.00

3.00

Soybean Oil

7.00

9.00

Maleated Soybean Oil

1.00

4.00

Polymer JR30

0.20  

 0.60

PEG (6) Caprylic/Caprylglycerate

3.00

5.00

Myristic Acid

0

3.00

Palm Kernel Acid

2.00

0

Glycerine

2.00

4.00

Perfume

1.00

2.00

Preservative

0.10

0.30

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Many other variations are possible; the main problems are achieving a satisfactory viscosity with adequate foaming and leaving a residual emollient film on the skin. Many of the emulsions are stabilised by liquid crystalline structures so mixing with excessive shear is to be avoided. Patent USP 6,606,608 suggests the emollient effect is due to larger than usual droplets of the lipid phase within the aqueous cleansing phase and lays claim to compositions whereby the moisturising phase comprises from about 1% to about 30% by weight of the composition of lipophilic skin moisturising agents comprised of droplets having a particle size distribution such that at least about 50% by weight of the droplets have a diameter of at least about 200 microns.

1.                Pharmaceutical Formulas, The Chemist and Druggist, London, 1934

2.                Pharmaceutical and Cosmetic Preparations for Topical Administration; Morrison & Gibb, 1969

3.                Evison, J., New Product Introductions; SCS Spring Symposium 2000.