Creative Developments (Cosmetics) Limited

Sun Care SPC 2001

The table [attached] shows the materials that may be used as UV filters in cosmetic products in the EEC. Not all of these are acceptable in the USA, Japan, Australia or other major markets and different maximum levels may apply to those that are universally approved. Patent positions, safety considerations, solubility problems, incompatibilities with other ingredients or with the packaging and poor cost-effectiveness further restrict the numbers that a formulator will use. Despite these limitations new products are being continuously developed and the challenge is to obtain the maximum benefit from the lowest level of active.

The excitement for the formulator is that product improvements may readily be determined by in-vitro measurements, which although not sufficient for supporting the SPF label claim, are adequate for making comparisons in the laboratory. It may be that having ready access to objective determinations is part of the reason for so much activity in this area of cosmetic formulation.

First know the SPF and UVA/UVB ratio required and select the filter or filters to deliver those attributes in the product form preferred. The majority of actives are oil-soluble and many have limited solubility so the next stage is to ensure that the selected filters are soluble in the base and will remain dissolved throughout the shelf life of the product. It is important that the emollients have the correct spreading characteristics and Cognis has further developed its cascade theory of emolliency and incorporated it into Synergistic Sun Systems [Ref 1]. It describes the interactions between UV absorbers, pigments and cosmetic raw materials and the effects of emollients on sensorial characteristics and SPF values. Chart 1 [attached] is an amalgam of solubility data supplied by Cognis and Chart 2 [attached] shows the boost in SPF values achieved by the authors in a test formulation.

Many materials enhance the rheological properties and hence the SPF of sun products. Gel Base BSM5™, Brooks Industries, is a polymeric solution of dimethicone and phenyl trimethicone that forms a substantive and water-resistant film on the skin and which can improve dispersion and feel of inorganic oxides on application. Diisostearoyl trimethylolpropane siloxy silicate, a silicone ester from A&E Connock is an efficient solvent for organic sunscreens and enhances the water resistance and SPF values of both organic and inorganic based preparations. Work by the author [REF 2] demonstrated the importance of good dispersion of the inorganic oxide in a suitable vehicle and a paper published by Connock [REF 3] shows a significant increase in SPF values when silicone esters form part of the non-aqueous phase.

A paper describing synergistic effects given at the IFSCC Congress, Berlin 2001 by Thomas Wünsch [Ref 4] concentrated on improving product performance by careful attention to the base formulation. Wünsch advocated an emulsion as the preferred vehicle with the use of UV filters in the oil phase. The selection of filters is important but the rheology and particle size of the emulsion droplets are also significant criteria in maximising SPF values. It is essential to have sufficient thickness of product film on the skin and this is achieved by imparting the proper rheological properties to the product. Good spreading characteristics are necessary but excessive thixotropy is to be avoided. Wünsch also described the problem of saturation whereby a filter may impart a relatively high SPF at low concentration but increasing the level of filter achieves little extra benefit. Traditionally this problem is overcome by using a cocktail of actives but many combinations are disappointing, however Wünsch found a mixture of 2.0% octyl triazone with 5.0% zinc oxide to be particularly effective.

A poster [Ref 5] at the IFSCC Congress described a factorial design for investigating synergistic responses between the UVB absorber, dioctyl butamido triazone and the UVA absorber, butyl methoxy-dibenzoylmethane (BMDBM). The conclusions supported those of Wünsch; that a small concentration of a UVA absorber could show a significant synergy with higher levels of UVB filters.

Finding synergy between organic and inorganic filters has also been a productive avenue of investigation over recent years. W. Johncock of Haarman & Reimer, manufacturers of the Heliopan range of organic filters, investigated mixtures of zinc oxide with octocrylene and with isoamyl p-methoxycinnamate and found significant increases in protection. J. Hewitt, Uniqema Solaveil, has published the results of extensive investigations into the factors affecting efficacy with microfine oxides [REF 6]. It was found that pre-dispersed systems have advantages over powder forms of TiO2, and that choice of emollients and emulsion rheology can have important effects on SPF. Hewitt and Housley also studied the synergy that may be obtained when using inorganic oxides in conjunction with OMC and other organics [REF 7].

The photostability of sun products used to be taken for granted but it is now realised that photo-instability is responsible for many apparent failures of formulation and it is also known that the products of photo degradation can be responsible for allergic irritation. A poster [REF 8] at the IFSCC Congress described switches between isomeric structures by cis-trans-isomerisation or by intramolecular H-transfer when a molecule is absorbing UV radiation as the cause of instability. The authors investigated the stability of a number of filters in w/o and o/w emulsions when subjected to irradiation from 0 to 50 MED. They were first tested individually, then in combination. Alone, BMDBM showed almost 100% degradation while bis-octoxyphenol methoxyphenyl triazine (BOMT) was almost 100% stable. Ethylhexyl cinnamate (OMC) and 4-methylbenzylidene camphor (MBC) were somewhere in between but at 20 MED both had lost more than 60% of their original concentration. Mixtures of BMDBM and of OMC with different filters were then tested. It was found that OMC does not improve the photo-stability of BMDBM and OMC is adversely affected by the presence of BMDBM. The photo-stability of BMDBM was improved with MBC and was not itself adversely affected.

Thus the formulator has to study the solubility of the sunscreen, look for synergy between filters, evaluate the rheological and sensorial characteristics of the vehicle and be cognisant of the photo-stability of the active ingredients. Turning to ingredient suppliers for help is often the next step and can be very productive. Materials such as OMC or benozphenone-3, whatever the source, should be chemically identical, however different suppliers provide it in different physical forms. Brooks Industries supply a sub-micron emulsion concentrate (SMEC) with UV Filters, which is a mixture of OMC, Benzophenone-3 and octyl salicylate in an emulsion with a particle size below 150 nanometers. Diluted to twice its volume with water it provides a liquid of SPF 15 to which other ingredients may be added to present a finished product. Brooks suggest a fennel (Foeniculum vulgare) seed extract that is a natural source of the enzyme peroxidase as a free radical scavenger to prevent lipid peroxidation and it also reduces the erythema response.

Sol-Gel Technologies has developed a novel process whereby organic sun filters are encapsulated in minute glass beads. [Photo attached] By isolating the active from other ingredients many of the problems of photo-instability, potential irritation and ingredient incompatibilities are avoided. A 35% active suspension of OMC has been extensively tested and it is shown that skin penetration of OMC is negligible and the safety profile of the material is excellent. I am informed that the planned capacity for this year is about 1 ton active ingredient a month, i.e. about 3 tons of a 35% suspension, and that capacity will increase next year.

The use of microfine inorganic oxides as sunscreen materials continues to expand as the safety and photo-stability of these materials is confirmed. BASF has acquired the Z-Cote brand of zinc oxide dispersions to add to its portfolio of Uvinul organic and inorganic filters. Z-Cote is a hydrophilic white powder and Z-Cote HP-1 is zinc oxide treated with dimethicone to render it hydrophobic. Uvinul TiO2 is titanium dioxide coated with trimethoxycaprylylsilane to improve dispersion in oil and silicone-based systems. Kemira surface treats titanium dioxide to provide readily dispersed versions under the UV-Titan trade name. UV-Titan XIII is coated with alumina and is water-dispersible while X170 is surface treated with alumina and dimethicone, which renders it hydrophobic and suitable for oil and silicone based products. The average crystal size of these two materials is.14 nm, which assures their transparency. Grade X610 is a mixture of two crystal sizes and is recommended for skin care and cosmetic formulations.

Uniqema Solaveil continuously improves the quality and variety of its titanium dioxide and zinc oxide dispersions. Small distribution of particle size maximizes the absorption efficacy at the critical wavelengths while reducing the tendency to whitening that was once a problem with all microfine oxides. Latest grades of titanium dioxide include 50% dispersions in most of the commonly used esters and silicone compounds and aqueous dispersions with various preservative systems. When formulating with microfine oxides a mixture of titanium dioxide and zinc oxide assures a high SPF in association with good UVA protection. Using an oil-based dispersion of zinc oxide with an aqueous dispersion of titanium dioxide simplifies formulation by reducing the solids loading in any one phase.

Decorative cosmetics have been much improved by the use of minute polymeric spheres such as Dry-Flo™ (aluminum starch octenylsuccinate) from National Starch, PMMA (polymethyl methacrylate) from Cardre Inc. and 3M Cosmetic Microspheres™ (magnesium silicate) also available from Cardre. The author prepared a w/Si makeup incorporating 15% Tioveil CM, a 33% dispersion of titanium dioxide in cyclopentasiloxane, which resulted in SPF 12.3. The addition of 3% Dry-flo increased the SPF to 17.30; 3% Cardre PMMA gave SPF 20.0 and 3% Cosmetic Microspheres resulted in SPF 24.70. Investigation of these materials in w/o and o/w emulsions is underway and has met with encouraging results.

Time-release of actives would appear to be particularly appropriate for sunscreen products as maintaining the protective film throughout the claimed safe exposure time is of paramount importance. Lexorez™ materials from the Inolex Chemical Company are a series of trimethylpentanediol/adipic acid copolymers with good solvent powers for oil-soluble sunscreens that are substantive to skin as a water-resistant film. By altering the cross-linking of the polyester and the terminal group on the backbone the polymer properties are adjusted and may be used for slow release of sunscreen actives [Ref 9]. Nanospheres™, Exsymol, are small particles of highly porous polymer that can be loaded with active ingredients. This provides a substantive material with a time-release mechanism and 100g of Nanospheres OMC contain1016 nanospheres.

Although everyone should be aware of the dangers of over-exposure to sunlight most white-skinned Europeans still covet a suntan. By accelerating the pigment darkening response to UV radiation a suntan may be acquired in less exposure time. Phycolanine™ from SECMA is a suntan stimulator derived from the brown seaweed, Laminaria ochroleuca. It is said to strongly stimulate tyrosinase activity to promote an even golden tan. Exsymol provides a copper acetyl tyrosinate methylsilanol complex as a suntan stimulator in a surfactant-free emulsion. Trade named Emulzome Tyrosilane C, the emulsion may be added to water or oil-based gels and it has a similar activity as tyrosinase on application. Emulzome Solaire™, a mixture of OMC and benzophenone-3 in emulsion form and other combinations are also available from the same supplier.

Finally, having formulated the optimum vehicle for the selected filters, attained synergy between actives while avoiding photo-instability and overcoming all the other pitfalls of product formulation it is advisable to review the patent situation before embarking on expensive in-vivo testing. References to some recent patents are to be found below.

1 Synergistic Sun Systems, Cognis

2                     Woodruff J.; Formulating sun care products with micronised oxides; Cosmetics and Toiletries Manufacture Worldwide 1993

3                     Connock A, The use of silicone esters in enhancing SPF values of inorganic sunscreens. A&E Connock (Perfumery & Cosmetics) Ltd.

4                     Wünsch T., Synergistic effects with high performance UV-Filters XXI IFSCC International Congress 2000, Berlin

5                     Ferrero L., Pissavini M., Perichaud C., Zastrow L., Experimental design application to sunscreen products. Demonstration of a synergistic effect between UVB and UVA absorbers. Ibid

6                     Hewitt J., Woodruff J., IFSCC Magazine, Vol.3 No.1, pp.18-23 (Jan/Mar 2000)

7                     Hewitt J., Housley S.,. Cosmetics & Toiletries Manufacture Worldwide 2000, pp292-297.

8                     Herzog B., Sommer K., Investigations on photostability of UV-absorbers for cosmetic sunscreens, XXI IFSCC International Congress 2000, Berlin

9                     D Smith et al, Polymeric ester technology for photoprotection enhancement; European UV and Sunfilters Conference, Paris, 1999.

USP 6,030,629 Photoprotective cosmetic/dermatological compositions comprising synergistic admixture of sunscreen compounds

USP 6,048,516 Light-screening agents

USP 5,955,091 Photobluing/whitening-resistant cosmetic/dermatological compositions comprising TiO2 pigments and deformable hollow particulates.

USP 5,770,183 High SPF (30 and over) waterproof sunblock compositions

USP 5,866,148 Photoprotective compositions comprising mutually incompatible oily dispersed phases