Creative Developments (Cosmetics) Limited

Sun Care 1999

As I write it is the start of National Sun Awareness Week; it is the end of May, the sky is dull and overcast and last week confirmed that the English summer consists of three sunny days and a thunderstorm. It is little wonder that, in Britain at least; the question is more one of whether a suntan is possible rather than an awareness of the dangers of solar radiation.

An article in the Daily Telegraph [Ref. 1] describes the results of taking photographs of the skin with an ultra-violet camera that exposes pigmentation damage caused by the sun. The writer said she felt that she had aged ten years when shown her photographs and that she was now truly aware of the dangers of exposure to sunlight. The same feature quotes two dermatologists: Dr Susan Mayou who said that “What has failed to sink into our tan-obsessed minds is the need for everyday protection” and Professor John Hawk. “We should all be using a moisturiser with a sun protection factor of 15 daily from early spring until the end of October”.

The Cancer Research Campaign reports that about 40,000 new cases of skin cancer are being reported annually in the UK and that the figures are rising. They estimate that if children used adequate sun protection up to the age of 18 then cases of skin cancer would be reduced by 70%. Yet despite public awareness campaigns the growth in sales of sun protection products are reported as being almost static in Europe and although the trend is towards higher SPF products 20% of sales are still for SPFs in single figures. Whether increasing use of daily skin care products with sun protection is in part responsible for the lack of growth in traditional sun products is not clear.

Despite the slowness of the buying public to follow advice about sun protection dermatologists and chemists continue to investigate solar damage and methods of limiting it and this interest is apparent in the papers presented in recent symposia. The entire first day of the 1998 IFSCC Congress [REF 2] was devoted to skin ageing and the sun with the emphasis on free radical formation and measuring the damage this causes in the dermal layers. Following the opening paper by Dr Tony Chu on the effects of solar radiation the European UV Sunfilters Conference [REF 3] concentrated on the practical formulation aspects of reducing sun damage. According to Chu [REF 4] the most serious effects of sun exposure are the chronic ones of skin carcinogenesis and photoaging. Skin carcinogenesis involves direct and indirect damage to cellular DNA that will allow malignant transformation of the cells and impairment of the skin immune system so that newly developing neoplastic cells are not recognised by the immune system and destroyed. Direct damage occurs because DNA absorbs ultraviolet light with resultant gene damage while indirect damage is caused by free radicals and singlet oxygen. Chu described these mechanisms and the role of the Langerhans cells in fighting damage to the immune system that includes recognising and destroying malignant cells. Unfortunately the function of Langerhans cells is impaired by UV radiation and their numbers are reduced so the radiation that is the cause of carcinogenic change is also responsible for reducing the bodies natural defence mechanisms.

Since their introduction some ten years ago the use of microfine inorganic oxides has proliferated in sun protection products. Several papers at the European UV Sunfilters Conference described different aspects of these materials and improved production techniques coupled with a better understanding of their properties has substantially contributed to their commercial success. At first they were introduced as alternatives to organic filters but are now increasingly seen as having a synergistic action when properly formulated in conjunction with traditional filters. A paper by Julian Hewitt [REF 6] underlined the benefits that accrue from such an approach. According to Hewitt the use of the inorganic oxide reduces the quantity of potentially irritating organic sunscreen required while the presence of the organic filter enables high SPF results to be achieved without the whitening effect that can result from high concentrations of inorganic oxide. Hewitt described the use of a dispersion of titanium dioxide in conjunction with octyl methoxycinnamate (OMC). While the SPF to be expected from 4% coated titanium dioxide is about 9 – 10 and that for 1% OMC about 2 – 3, when used in conjunction the results were >15. Further experiment showed that there was an improvement in the photostability of the OMC. While titanium dioxide is used for obtaining high SPFs zinc oxide is useful for providing UV-A protection. The two oxides are often used in combination to provide broad-spectrum protection but there can be problems with such a high solids content in the formula. Hewitt showed that the use of zinc oxide in combination with OMC boosted the expected SPF from about 15 to >22 while the presence of zinc oxide increased the UVA/UVB ratio from 0.17 to 0.42.

The Sun Protection Conference [REF 7] focused on labelling and regulatory issues as well as formulation and safety testing. World-wide changes in legislative requirements were described by Debra Redbourne [REF 8]. In Australia sunscreens are classified as drugs and must comply with the Therapeutic Goods Act. Two years ago the maximum claimed SPF was raised from 15 to 30 and if the product complies with specific tests it may claim broad-spectrum protection. Claims for water-resistance must be shown with a qualifying time and the actives must be listed with their percentage in the composition. The USA also classes sunscreen products as drugs and they must comply with FDA’s OTC monograph for Sunscreen Drug Products. Changes in some of the American regulations are under way and producers are urged to study the latest regulations. It must also be remembered that the maximum levels of actives allowed differ from country to country. The regulations in Japan are similar to those in force in the EU in that sunscreen products are classified as cosmetics and the actives used are from a positive list. In the EU there are nineteen fully permitted UV filters although their concentration and areas of application are limited. Two new materials have recently been added to the permitted list, dioctyl triazone and drometrizole trisiloxane although use of the latter is severely restricted by patent applications.

How high should the SPF be is a frequent query; Australia limits the quoted value to 30 but most other countries allow free rein to claims with a product in Japan claiming SPF 123! A paper by Peter Finkel [REF 9] endeavoured to introduce common sense to the claims. His first point was that the maximum amount of radiation expressed as the minimal erythemal dose (MED) that can reach sensitive skin during one day of sunshine is 32MED/day although realistically this would be lower. For adequate protection an SPF of 15 – 20 would be sufficient, however natural variations in application can result in large deviations in actual SPF and loss through abrasion and perspiration can further reduce the protection received. Finkel concluded that products claiming SPF 20 – 30 were justified but because of the difficulties in measurement anything above 30 is virtually meaningless. It should be remembered that SPF 20 blocks 95% of the erythemal active radiation, SPF 50 blocks 98% and SPF 100 stops 99%.

Even more controversial is the subject of UVA protection. Dermatologists believe that high SPF values without significant UVA protection are a major cause of radiation-induced skin problems. Sunburn is a natural warning signal to stay out of the sun. Without it sun product users are exposed to UVA radiation for far longer periods than would normally be the case. Finkel reported that currently there are four in-vitro methods and four in-vivo methods of determining UVA protection in general use. Finkel fears that producers will resort to the method that gives the highest number resulting in even more confusion for the consumer.

It is well known that the base can affect the sunscreen efficacy. Dr William Johncock has described some of the problems that range from OMC turning products bright yellow if packed in clear bottles to the formation of long needle-like crystals if the pH of a product containing phenylbenzimidazole sulfonic acid falls below 7 [REF 10]. Octyl triazone, butyl methoxydibenzoylmethane, benzophenone-3 and methylbenzylidene camphor crystallise if they are insufficiently solubilised and polar fatty acid esters should be considered to improve solubility. The solubility parameters of most liquid UV filters is between 9 and 10.3, which is similar to that for the polymers used in many packaging materials. This can result in the filter migrating into the plastic with a consequent degradation of the pack and loss of active in the formulation.

Not all reactions between base and active are negative and in many instances the SPF of a given combination of sunscreens may be significantly enhanced. This may be achieved by affecting the rheology of the product and improving the spreading effects and the nature of the film deposited on the skin or by improvements in solubilising the sunscreen. Data published by Th Goldschmidt shows that adding 1% of cetyl dimethicone to a w/o cream containing 3% OMC increased the SPF from 11.5 to 13 and when added to a w/o lotion containing 5% titanium dioxide the SPF increased from 11.8 to nearly 14. A combination of titanium dioxide (3%) and OMC (3%) gave an SPF of 9.1 but when 0.25% cetyl dimethicone was added this was increased to 13.5. It is suggested that the emollient and film-forming properties of cetyl dimethicone contribute to this increase. The results are similar to those found by A&E Connock when working with the silicone ester, diisostearyl trimethylolpropane siloxy silicate. When used in a o/w formulation containing 5% microfine titanium dioxide the SPF increased from 12 to >15 (Formula 1).

There have been recent introductions of w/o emulsifiers and these can substantially aid the preparation of water-resistant formulations. From Th. Goldschmidt diisostearoyl polyglyceryl-3 diisostearate may be used for the preparation of both lotions and creams. It is non-ionic and is effective at 3% for the preparation of w/o emulsions with an oil phase of between 20 – 35%. It can be used to emulsify polar oils and the resultant compositions show good spreading properties making it ideal for the preparation of sunscreen emulsions. A w/o emulsifier introduced by Uniqema is PEG-30 dipolyhydroxystearate. Added as approximately 10% of the total oil phase it is used for the preparation of stable w/o emulsions containing approximately 10 – 30% oil phase. Viscosity may be adjusted by varying the volume of the internal phase or by the addition of waxes and it is effective with both polar and non-polar oils and is alcohol-tolerant. The writer has made extensive use of this emulsifier in the preparation of sun protection products based on microfine titanium dioxide dispersions and has had excellent results. It is of interest that a basic formula when thickened with microcrystalline wax and incorporating 5% titanium dioxide has an SPF of about 12. If beeswax is used instead the SPF increases to about 16 and by judicious choice of emollient this may be enhanced to 18 – 20 (Formula 2).

The C.P. Hall Company has recently introduced a number of emollient esters that are effective solubilisers for many sunscreen actives. Butyloctyl salicylate is a low viscosity oil that solubilises avobenzone (butyl methoxydibenzoylmethane) and benzopheneone-3 and enhances the photostability of avobenzone. Hexadecyl benzoate and butyloctyl benzoate have similar solvent properties and are said to be more lipophilic and emollient than similar benzoate esters and diisopropyl sebacate and diisopropyl adipate are both good solvents that form non-occlusive films and are soluble in ethanol. A paper by Craig Bonda (REF 11) describes the formulation of stable, high SPF , broad spectrum sunscreens with avobenzone that illustrates the use of butyloctyl salicylate, hexadecyl benzoate and butyloctyl benzoate to photostabilise avobenzone and mixtures of sunscreens that contain it.

Finetex has long been known for its benzoate ester, C12-15 Alkyl Benzoate. It has now combined this with dipropylene glycol dibenzoate and PPG-15 stearyl ether benzoate to form a unique proprietary blend that is described as an exceptional solvent for sunscreen actives. It can dissolve up to 30% benzophenone-3 and 16% Avobenzone. It is also said to provide a soft, smooth and non-greasy skin feel with excellent tactile properties. Finally spray-on sun protection emulsions are in vogue. From Brooks Industries is a new sub-micron sunscreen concentrate. Trade named SMEC Sun, it may be diluted with water to produce a milky sprayable emulsion. A 1:1 dilution provides SPF15 protection, which is rapidly absorbed into the skin without leaving a greasy feel.

1. Catherine O’Brien; When the camera does the talking; Daily Telegraph, 31/05/99

2. IFSCC Congress 1998; Cannes, France.

3. European UV Sunfilters Conference 1998; Paris, France

4. Tony Chu; The effects of solar radiation, ibid.

5. David Fairhurst; Sunscreening properties of microfine zinc oxide, ibid.

6. Julian Hewitt; Novel formulation strategies for high SPF and broad spectrum sunscreen products, ibid.

7. Sun Protection 1999; London, England.

8. Debra Rebourne; Changes in legislative requirements, ibid.

9. Peter Finkel; Sun protection factor and UVA protection labelling in Europe, ibid.

10. William Johncock; Favourable and unfavourable interactions in sunscreen formulations, ibid.

11. Craig Bonda; Formulating stable, high SPF , broad spectrum sunscreens with Avobenzone, The C.P. Hall Company

Formula 1

Material	%	Trade Name	Supplier
Diisostearyl trimethylolpropane siloxy silicate	5.00	AEC DTSS	A&E Connock Ltd.
Dimethicone	2.00	Generic
Potassium cetyl phosphate	0.50	Amphisol K	Roche
Titanium dioxide dispersion in C12-15 alkyl benzoate	10.00	Tioveil 50 FIN	Uniqema Solaveil
Hydroxyoctacosanyl Hydroxystearate	3.50	AEC Hydroxyoctacosanyl Hydroxystearate	A&E Connock Ltd.
Sorbitan Palmitate	3.50	Generic
Aqua (water), pure	To 100%
Xanthan Gum	0.20	Generic
Magnesium Aluminum Silicate	0.80	Veegum Ultra	R.T Vanderbilt Co Inc
Propylene glycol	5.00	Generic
Polysorbate 20	3.50	Generic
Perfume, preservatives etc. as required.
Mixing: This is an o/w emulsion. The hot oil phase (70C) is added to the hot Aqueous Phase (70C) with mixing and the mix stirred down to 25C. It should then be homogenised. Generic materials may be purchased from A&E Connock Ltd., or from your local supplier. In-vitro SPF 1

Formula 2

Material	%	Trade Name	Supplier
Octyl Stearate	17.50	Cetiol 868	Care Chemicals
Cera Alba (Beeswa	3.00	Generic
PEG-30 Dipolyhydroxystearate	2.60	Arlacel P135
Titanium dioxide dispersion in C12-15 Alkyl Benzoate	10.00	Tioveil 50 FIN	Uniqema Solaveil
Aqua (Water), pure	qs
Magnesium Sulfate	0.70	Generic
Propylene Glycol	5.00	Generic
Perfume, preservatives etc. as required.
Mixing: This is a w/o emulsion. Heat both phases to 70C and add the hot Aqueous Phase to the hot oils with brief high shear mixing, stir down to 25C and briefly homogenise. This simple starting formula is water-resistant and has an SPF of 20+ (in-vitro).