Issue 21
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Introduction

In the past few years the market for sun care products has been dominated by high SPF products. A general trend for special products with sun protection factors of up to 60 was observed. Experience has shown that dermatological and sensoric factors are not the only factors determining the influence of a formulation matrix on the efficacy of sun care products. Rather, we have to make use of synergistic interactions between cosmetic raw materials and UV filters in order to realize products, especially high SPF products, under economic aspects.

New emulsification technologies, innovative emulsifiers and emollients, as well as active ingredients with polyfunctional and synergistic performance characteristics have recently been described with the “Synergistic Sun System” concept proposed by Rolf Kawa and co-authors (1). Kawa shows that profound knowledge of the spreading behavior of the emollients used is required to formulate elegant cosmetic sun care products with balanced sensorics and that they may be formulated with the “Spreading Cascade” concept. Furthermore, Kawa describes that the selection of emulsifiers, oils and active ingredients is determined by its performance regarding emulsification, pigment dispersion, UV filter solubility and dermatological compatibility.

Expectations of innovative emollients for sun care

In addition to caring properties emollients have to display excellent solution and dispersion properties for UV filter and pigments and must have the capacity to increase the level of the SPF. Furthermore, they must have excellent spreading properties and a positive influence on the total sensorics of the formulation.

In order to formulate stable and effective sun care products, crystalline UV filters must completely dissolve in emollients and remain dissolved in them. The solution properties of various oils was tested for two crystalline UV filters. The tests showed that the emollients Cetiol B (2) and Myritol 331 (3) may dissolve the UVB filter 4-Methylbenzylidene Camphor and the UVA filter Butyl Methoxydibenzoylmethane in high concentrations (Figure 1).



The chances of subsequent recrystallisation are reduced and instability of the formulation connected with this, as well as a reduction of the sun protection factor, can be avoided.

Microfine titanium dioxide and zinc oxide are gaining further importance for use in cosmetic sun care preparations. The correct incorporation of these substances requires that the developer is experienced with regard to galenics. He must avoid an agglomeration of the pigments, leading to a loss of effectively of the emulsion. A deep knowledge of the dispersing properties of the emollients is necessary since the appropriate ones are to be selected in order to achieve a homogeneous and permanent distribution of the pigments, thus counteracting agglomerations. It has been shown that the polar emollient Myritol 331 has a particularly positive influence on the distribution of pigments and that it largely contributes to the stability of a pigment-containing sun care emulsion.

Furthermore, it was noted that the polarity of the emollients influences the level of the UV absorption of organic UV filters. This result was confirmed by a model formulation in vivo. The tests showed that the SPF value is significantly increased from 8 to 11 if Myritol 331 is applied instead of an unpolar emollient.

The spreading behavior of a cosmetic emollient is a major and objective criterion for the sensoric properties of a sun care emulsion. An even spreading of the emulsion is furthermore an important criterion for the homogeneous distribution of the UV filters applied on the skin. Ideally, only slowly spreading UV filters are combined with fast-spreading oils and medium-spreading oils to form a “Spreading Cascade” in order to avoid gaps in the feeling of smoothness (Figure 2).


A good knowledge of the spreading properties is especially useful when sun care product ranges with various SPF’s have to be adapted sensorically. In order to compensate the negative sensoric properties of the UV filters at increasing SPF’s, it is necessary to increase the proportion of high spreading oils, e.g. Cetiol OE (4) or Cetiol B and to combine them with medium-spreading oils such as Myritol 331 or Cetiol PGL (5). Thus, a constant sensoric profile may be preserved for a complete product range despite of varying SPF’s.

Expectations of innovative cosmetic emulsifiers for sun protection

In practical use, sun care emulsions are frequently exposed to high temperatures. This requires emulsifiers with an excellent stabilising potential for the interface, even at higher temperatures, independent of the polarity of the formulation components applied.

Eumulgin VL 75 (6), a mixture of Lauryl Glucoside and Polyglyceryl-2 Dipolyhydroxystearate, a hydrophobic stabilising synergist, was tested under this aspect. This new, vegetable-derived and dermatologically highly compatible, O/W emulsifier shows a high emulsification potential for emollients of various structures. In particular, an emulsion containing Myritol 331, the sun care properties of which are granted by its excellent solution, dispersing and booster properties, is fine-disperse. Polar UV filters such as Octyl Methoxycinnamate are emulsified with an excellent fine disperse character. Due to their low-viscous consistency, sun care emulsions may be realised with the new emulsifier by cold emulsification. Figure 3 describes a formulation of a cold emulsified O/W sun milk (SPF 15) with even spreading properties.

Figure 3
O/W sun milk SPF 15 (cold emulsification)          Formulation No . 98/031/2
Component	INCI	%
Cetiol® OE	Dicaprylyl Ether	3,0	fast
Myritol® 331	Cocoglycerides	13,0	medium
Eusolex® 2292	Octyl Methoxycinnamate	7,0	slow
Copherol® F 1300	Tocopherol	1,0	slow
Eusolex® 4340	Benzophenone-3	3,0
Silicone Oil	Dimethicone	0,5
Carbopol® ETD 2001	Carbomer	0,3
Eumulgin® VL75	Polyglyceryl-2 Dipolyhydroxy- stearate,Lauryl Glucoside, Glycerin	3,5
Hydagen® B	Bisabolol	0,2
Glycerin	Glycerin	3,0
Water	Aqua	64,8
KOH (20%)	Potassium Hydroxide	0,7
Fragrance, Preservation		q.s.
©Skin Care Forum

Besides their high protective and caring effects, W/O emulsions also display another advantage, namely water resistance. By applying the W/O emulsifier Dehymuls PGHP (7), concepts of light and sensorically sophisticated sun care emulsions may be easily realized independent of the polarity of the formulation components used.

PIT (PhaseInversionTemperature) emulsions represent an innovative technology for new sun care applications. These are water thin O/W emulsions, which enable sprayable applications. The PIT technology is based on the knowledge that O/W emulsions with nonionic ethoxylated emulsifiers display different types of phase behaviour in dependence on composition, structure and concentration of the emulsifier as well as on temperature. The degree of temperature determines whether the emulsifier is enriched in the aqueous or in the lipid phase. In the transition area, i.e. the phase inversion temperature, the interface tension is reduced to a minimum. Microemulsions form spontaneously and without any particular mechanical addition of energy. Even after cooling down to room temperature they have a very fine droplet distribution of an average of 100-300nm. They are water thin, and extremely phase stable, which is due to their very small interior phase. Production technical steps are reduced to warming, simple stirring and cooling down (10). The principle of the PIT technology is shown in Figure 4.

Active ingredients for sun protection products

Besides the basic components described which may significantly improve the performance of a sun care formulation, active ingredients enhance such effects as water resistance, skin care and regeneration and protect it from free radicals. Examples of this are chitosan and tocopherol.

Hydagen CMF (8), the cationic substantive biopolymer of marine origin functions as a film former and significantly improves the water resistance of sun care formulations. Furthermore, it has a positive influence on the sensorics of an emulsion and thus improves the following parameters: softness, smoothness and skin compatibility.

Besides numerous biological functions vitamin E also has a high autoxidative potential and thus is applied in sun care products to avoid the formation of a papulous polymorphous light dermatosis (“Mallorca acne”). The Institute for Experimental Dermatology at the University of Witten-Herdecke demonstrated in a study that peroxides which may form from the emulsion components under the influence of sunlight are of significance for the formation of the papulous polymorphous light dermatosis. The study further demonstrates that the reaction of the skin in dependence may be decreased in dependence of the concentration of the antioxidant Controx KS (9) applied in the emulsion.

Summary

Figure 5 shows a selection matrix of the various aspects that are of significance in the formulation of sun care products. From a glance you can see that all of the suggested raw materials are polyfunctional and that future concepts should be developed to integrate polyfunctional ingredients which allow the change from a sun care formulation into a “Synergistic Sun Care System.”

Reference and INCI Names

(1) Kawa, R.; Ansmann, A.; Jackwerth, B.; Leonard, M.; Das Synergistic-Sun-System-Konzept: Synergien in der Formulierungswelt kosmetischer Sonnenschutzprodukte nutzen, Parfümerie Kosmetik 80, No. 3 (1999) 17-18, 20, 22-23
(2) Cetiol B: Dibutyl Adipate
(3) Myritol 331: Cocoglycerides
(4) Cetiol OE: Dicaprylyl Ether
(5) Cetiol PGL: Hexyldecanol (and) Hexyldecyl Laurate
(6) Eumulgin VL 75: Polyglyceryl-2 Dipolyhydroxystearate, Lauryl Glucoside, Glycerin
(7) Dehymuls PGHP: Polyglyceryl-2 Dipolyhydroxystearate
(8) Hydagen CMF: Chitosan Glycolate
(9) Controx KS: Tocopherol (and) Hydrogenated Palm Glycerides Citrate
(10) Siehe auch: Förster, Th.; PIT Emulsions, Skin Care Forum No. 2 (1992); Strey, R.; Microstructure of Microemulsions, Skin Care Forum No. 14 (1996)
(11) Eumulgin PL 68/50: Cetearyl/Glucoside (and) Cetearyl Alcohol
(12) Hydagen B: alpha-Bisabolol
(13) Generol 122 N: Soybean (Glycine Soja) Sterol
(14) Copherol F1300, 1250: Tocopherol/Tocopheryl Acetate

All products mentioned here are registered trademarks of Cognis.




In 1985 Rolf Kawa assumed a position in Henkel's application technology for raw materials for the cosmetic and pharmaceutical industries in Düsseldorf and was responsible for the development of new emulsifiers and emollients. Within the new Care Chemicals business unit, he is Head of the new global project sun care in the area of technical service for skin care products.

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