An Asia Pacific sun care market perspective

The combined trend toward sun protection and whitening indicates many Asian consumers use sun care products to maintain fair skin. Sun protection is typically provided by skin lotions and moisturisers containing sunscreens, and application is usually limited to the summer months. Most are formulated with an SPF of at least 15, except in Japan, where skin lotions claim very high SPFs, often in the range of 60 to 100.

Because consumers prefer a light complexion, and a tanned look is not considered fashionable. Self tanning and after sun products are not popular in the Asia Pacific region. Still, sales of sun care products continued to increase in 2005, with a growth of 16% for that period, due in large part to consumer education. South Korea ranked first in the Asia Pacific sun care market, with almost a 39.2% share, representing the fastest global growth – nearly 30% – in 2005.

Japan followed with a 31.8% share of the Asia Pacific sun care market, while China increased its share to 19.2%, representing a 15% growth in 2005. Use of silicones in sun care products continues to grow, and as silicone technology evolves, greater interest has focused on their multifunctional properties. In the newest sun care products and product forms, silicones can be used to provide substantivity, sebum control, resistance to wash-off and enhanced SPF. This article describes a new silicone material that can aid wash-off resistance in sun care products. It also summarises results of recent studies that demonstrate how silicones can enhance SPF values.

Improving wash-off resistance

Studies were conducted to evaluate the impact of new silicone acrylate copolymers on the wash-off resistance of ethylhexyl methoxycinnamate. Silicone acrylate copolymers have a distinctive structure based on a polyacrylate backbone and dendritic side chains.

The types of acrylic monomers and their combinations determine the degree of hydrophilicity or hydrophobicity, water or oil repellence, ingredient compatibility and hardness of films formed by these materials. Details of the wash-off evaluation method are described elsewhere1 but can be summarised as follows:

Materials:
Cyclopentasiloxane (and) acrylates polytrimethylsiloxymethacrylate copolymer.
Isododecane (and) acrylates polytrimethylsiloxymethacrylate copolymer.

Instrumentation and methods:
Wash-off simulatorb (Fig. 1).
Washing time: 180 seconds.
0.015 g of product for a circular area 3 cm in diameter.
UV filter measurement by UV spectroscopy.

Using this method, the impact of new silicone acrylate copolymers in comparison to cyclopentasiloxane (and) trimethylsiloxysilicate, a silicone resin, was evaluated using the test formulation in Table 1. This silicone resin was selected as a benchmark because it demonstrated good wash-off resistance in a previous study.

Figure 2 summarises the results as percent ethylhexyl methoxycinnamate washed away.

Results show the silicone acrylate copolymers (delivered by either a cyclopentasiloxane or isododecane solvent) can significantly improve wash-off resistance over the silicone resin. The film formed by the silicone acrylate is slightly more flexible and less brittle than the one formed by the silicone resin, making it stronger. Figure 3 illustrates the evaporation rates for the two solvents, which may suggest the appropriate choice for specific applications or volatility requirements.

Screening silicones for enhanced SPF

The materials, instrumentation and experimental protocols related to SPF screening and evaluation of wash-off resistance2 can be summarised as follows:

Materials:
A broad range of silicone technologies were evaluated, including organofunctional materials with polyether, carbinol and alkylmethyl functionality as well as variations in molecular weight, silicon:oxygen ratio and cross-linking.

Instrumentation and methods:
Labsphere UV-1000S ultraviolet transmittance analyser.c
Quartz substrate.
Product application: 2 mg/cm2.
Method of application: Meyer rod (Fig. 4).

Although silicones are used extensively in sun care products, this use has been limited to a few materials. Volatile and phenyl-functional materials are currently used in sun care formulations, especially for improving spreading and decreasing the greasy, oily feel imparted by organic sunscreens. Another functionalised family of silicone materials, alkylmethylsiloxanes, have been shown to significantly improve the SPF of both oil-in-water and water-in-oil systems.3 Silicone resins, high molecular weight silicone gums and elastomers are also well known for their positive impact on wash-off resistance when formulated into a variety of personal care products.4

In this study, an optimised in vitro SPF screening method, using a simple cream gel formulation, was used to evaluate of a number of silicone technologies for their impact on SPF. To provide additional validation, three commercial products with different in vivo SPFs were measured using the optimised in vitro SPF method. The results, shown in Table 2, showed good correlation between in vivo and in vitro SPF, indicating that the in vitro method is a good screening tool for identifying the impact of different silicones on SPF.

Approximately 100 silicone materials covering most chemical possibilities were screened using the cream gel emulsion in Table 3. The most relevant results are summarised.

The organo-functional materials all had a positive impact on in vitro SPF when formulated into the gel cream emulsion (Fig.5). However, two were particularly efficient, a rake silicone polyether (PEG/PPG 15/15 dimethicone) that is readily water-soluble, and a silicone carbinol fluid (bis-hydroxyethoxypropyl dimethicone), an oil-soluble polar silicone. Both are good wetting agents and might help by improving the film formed by the sunscreen, as well as ensuring better distribution of sunscreen droplets within the gel to allow more uniform film formation.

The second class of materials evaluated comprised silicone blends (Fig.6). Silicone elastomer performance was less than desirable, especially for the blend in volatile silicone. This could be due to the poor film-forming performance inherent to its elastomeric structure, or to its unique powdery feel. The impact of gum blends on the in vitro SPF of the gel cream was positive, especially for the gum in cyclopentasiloxane. This result is interesting because although these types of materials are known for their good film-forming properties to impart wash-off resistance, their inherent incompatibility with sunscreens did not make them an expected candidate for SPF improvement. The compatibilising impact of the cyclopentasiloxane could explain this result.

On the resin side, the good result obtained with cyclopentasiloxane (and) polypropylsilsesquioxane could be explained by the improved compatibility this resin has with sunscreen, compared to a trimethylsiloxysilicate resin. In addition, the new resin forms a very good film with similar wash-off resistance compared to the silicate, yet it has improved sensory characteristics.5

For the silicone materials screened using the optimised in vitro method, results demonstrated that depending on their nature, silicones have different impacts on in vitro SPF. Although no direct in vivo validation has yet been conducted, the in vitro method shows good correlation with commercial benchmark in vivo SPF values, making this method a good predicting tool for identifying trends in the impact of different silicones on formulation efficiency. It is important to note that the results shared in this article are specific for the type of formulation and ingredients tested. Results could be very different for other formulation types. Additional work continues in this regard and results will be communicated in the future.

Conclusions

The results of this study can provide bench chemists with a broader choice of silicone materials for developing innovative, high performance sun care products that also demonstrate superior aesthetics. These combined characteristics should encourage consumers of all ages to protect their appearance, health and overall wellbeing by increasing their use of sun care products.

The positive impact on sunscreen efficiency would also be valuable for skin care products in which there is a possibility of decreasing the quantity of sunscreens, leaving more flexibility for other actives and sensory enhancers. This approach can be of particular interest for the Asia Pacific market, where skin care products combine functional and sun protection benefits while maintaining a high aesthetic standard.

Footnotes

a Data on sales and market supplied by Euromonitor, 2006.

b The Simulator 700 is a product of Dia-Stron Limited, Andover, Hampshire, UK.