Delivering UV protection every day: novel ingredients and formulating approaches provide aesthetics as well as efficacy.

UV PROTECTION has become a factor in virtually every category of skin care products available on the market today due to increasing consumer awareness of the effects of sun exposure on skin. Sunscreen ingredients and technologies are no longer used only in "beach" products. Increasingly, UV protection is promoted as an additional benefit in products designed to be used every day, year-round.

Sun care products are used mainly to prevent sunburn or short-term effects of sun exposure with a quest for high SPF and moderate emphasis on the skin feel of the emulsion. There is a general consumer acceptance for a heavier, less-pleasing skin feel than there is for daily skin care products. On the other hand, the objective for the addition of sunscreens to daily skin care products is to provide protection from long-term effects of sun exposure, mainly aging and melanoma formation. Those sought-after benefits from the inclusion of sunscreens in daffy skin care products must be achieved without compromising the required lighter and softer skin feel of such products.

Therefore, consumer requirements for such daily-use products are somewhat different to those for beach products. In the latter case, high SPF is the most important priority; but in daily skin care, SPF requirements tend to be lower. While it is still important for a product to have good SPF efficacy, other aspects take on greater importance in daily use products, in particular:

* Cosmetic Elegance, The product must be easy and pleasant to apply, and must not leave any visible residue after rubbing in.

* Mildness. For every day products, it is especially important that the ingredients used are mild and non-sensitizing. This is particularly important for products designed for sensitive skin.

* Broad Spectrum Protection. This is now seen as a key requirement in all UV protection products, and especially so in daily use products.

Consideration of these requirements is driving development of new sunscreen actives, targeted specifically at the daily skin care market. However, such developments, and achieving the necessary regulatory approvals for these new materials, are costly and time-consuming. It therefore falls to today's ingredient supplier and the personal care formulator to bridge this technology gap through innovation in ingredient forms and new formulating approaches.

The product must have an aesthetically pleasing skin feel, and (except for pigmented products or for markets where a whitening effect is desired) should not be visible after application. The ingredients used should be as mild as possible, and the UV filters need to provide effective UVB and UVA protection. Achieving these objectives requires not only careful choice of the actives, but also of other components such as emulsifiers and emollients.

Choice of UV Filters

The first choice for the formulator here is: organic or inorganic? Both are capable of delivering high SPF efficacy, but how do they match up against the specific requirements of daily use skin care products?

Inorganic or "physical" sunscreens (titanium dioxide and zinc oxide) have two inherent advantages in this market. Firstly, they are very mild. Secondly, they both offer, in a single ingredient, UVB and UVA protection. Historically, however, inorganics tend to leave a white film on skin. If only a low SPF is required, say less than 8, this can be achieved by using about 3% (or less) of Ti[O.sub.2], and at such levels the whitening effect may be insignificant. However the current trend is toward SPF values of at least 15, even for daily use products; the levels of inorganic sunscreens required to reach such SPFs typically give a level of whitening that is unacceptable for such a product. It is for this reason that organic UV filters have been used much more than inorganics in daily skin care.

But now, new developments in inorganic sunscreen technology offer formulators the opportunity to take advantage of the benefits of Ti[O.sub.2], without sacrificing cosmetic elegance. A truly transparent inorganic UV filter is something which has, for some time, been a target for researchers working in this field. It has been shown previously that titanium dioxide can be made transparent to visible light if the particles are small enough; (1) unfortunately, as has been demonstrated, (2) such a material is also largely transparent to UVA and UVB light, and therefore has low efficacy as a sunscreen. Accordingly, this leaves something of a dilemma.

The answer to this dilemma has been found in a new production process for fine particle Ti[O.sub.2], which facilitates greater control of particle size distribution in the material produced. When combined with patented dispersion processes, the result is a dispersion of Ti[O.sub.2] in which the mean particle size is optimized for UVB protection, whereby the particle size distribution is very narrow, with no "oversize" particles. This means that, in a thin film, the Ti[O.sub.2] gives negligible attenuation of visible light.

This new Ti[O.sub.2] is available as either an oil-based dispersion, which has been previously reported, (3) or as a water-based dispersion. The latter product is unusual in that, although the carrier medium is water, the Ti[O.sub.2] particles have a hydrophobic coating. This new water-based dispersion was compared with other aqueous Ti[O.sub.2] dispersions in two formulations. Four different aqueous dispersions were incorporated into these formulations. The characteristics of these dispersions are shown in Table I (dispersion 1 is the new dispersion).

In the formulations, the content of Ti[O.sub.2] dispersion was adjusted in order to give equal Ti[O.sub.2] contents in the final emulsions. Figures 1 and 2 show in-vitro SPF and whitening data for the two formulations, made with each of the four dispersions. It is apparent that, as with any UV active, efficacy is formulation-dependent; dispersion 4, for example, gives a relatively low SPF in one formulation, but a good performance in the other. Dispersion 1 provides significantly better transparency (less whitening) than the other dispersions, in both formulations.

[FIGURES 1-2 OMITTED]

Interesting observations were noted during assessment of the skin feel of the final formulations. In a blind test, it was found that assessors could easily distinguish between formulations containing hydrophilic Ti[O.sub.2], and those with hydrophobic Ti[O.sub.2]. While formulations containing dispersions 2 and 3 (hydrophilic material) were described as "dry" with a "chalky" after-feel, those with dispersions 1 and 4 gave a smoother, more lubricating feel. In some cases the after-feel with the "hydrophobic" dispersions was described as "silicone-like."

Choice of Emulsifiers

Sunscreen formulations are challenging. Most ingredients will influence SPF and their selection is therefore as critical as the selection of sunscreens.

When formulating a daily use product with UV protection, the formulator is faced with the double challenge of achieving stability and aesthetics as well as good SPF. Key factors are the solubility and compatibility of the sunscreens and spreading on the skin; for makeup products, water-resistance can also be important. Consequently the right combination of emulsifier, emollients and other excipients is critical for a successful formulation.

Water in oil emulsions are the best option to deliver a uniform film on the skin, leading to better skin protection and SPF. As they are held together by lipophilic surfactants, they also provide better water-resistance profiles than standard O/W emulsions. Their disadvantages are the difficulty in the making of the emulsions, the cost, and the heavy, greasy skin feel. But a few surfactants, such as PEG-30 Dipolyhydroxy-stearate, allow for making W/O emulsions with sensorial and cost profiles close to those of O/W emulsions. A pinch of this very large polymeric surfactant makes W/O emulsions with internal phase ratio as high as 85%, thus giving a light and fluid W/O emulsion. This emulsifier also provides a considerable amount of dispersing property, which comes in very handy when formulating with solids such as inorganic sunscreens or pigments. Such W/O emulsions are best suited for dry skin facial formulation and for long-were makeup foundations.

O/W emulsions remain the more commonly-used form for daily skin care products; there are also some great alternatives to classical emulsifier systems.

One alternative is the use of low HLB O/W emulsifier systems. Prime examples are emulsifier systems designed to form a liquid crystal network in the bulk water phase, such as Sorbitan Stearate (and) Sucrose Cocoate. The liquid crystal network not only serves as a stabilizing system for the oil droplets but also provides a suspending medium for solids, such as aqueous dispersions of fine particle Ti[O.sub.2]. The uniqueness of this system resides in the large amount of bound water in the liquid crystals, which provides extra moisturization and a fresh sensation on the skin. This system is perfect for light lotions or creams and foundations.

A second alternative is newer, more sophisticated systems making O/W emulsions with a low amount of surfactants. These systems are based on polymeric stabilization, making use of a unique synergistic blend of polysaccharides (sucrose, mannan and xanthan gum). (4) This stabilizes emulsions at a very low use level and generates emulsions with unique and very interesting rheological properties. The emulsions are very fluid, extremely shear thinning and thixotropic. They are the ultimate choice for making sprayable emulsions that will spray as beautifully as water-thin emulsions without running and dripping down the skin and while maintaining a pleasant skin feel. They are best used to make fluid lotions and foundations, with soft and subtle creamy skin feel.

Another innovative emulsifier combination consists of a blend of ethoxylated alcohols (steareth-2 and steareth-21), with a biomimetic phospholipid. The combination of high and low HLB surfactants makes for beautiful classic O/W emulsion. The phospholipids for their part are unique cationic surfactants based on essential fatty acid (eg. linoleic acid or [gamma]-linolenic acid). They are great skin conditioners and skin smoothing agents, co-emulsifiers and potential release systems for the fatty acid to the skin. This system is a good option for a formulation positioned for mature skin, with added therapeutic advantages and effects.

Choice of Emollients

The world of emollients can indeed be a vast and confusing environment. There are many emollients to choose from, with one of the primary factors of selection being skin feel. The skin feel will be governed primarily by the viscosity and the chemical class--the main classes being esters, silicones, hydrocarbons and fluoro compounds. But there are various additional factors in the selection of emollients such as solvency, moisturization, substantivity, occlusivity, spreading, gloss, compatibility or surface properties.

These additional factors are of great importance and should be explored diligently when formulating with sunscreen actives. Positive effects on the skin, such as skin moisturization and skin elasticity, are tremendous assets, but crucial in this case are the effects of the emollients on the overall SPF of the formulation. Indeed, keeping all other ingredients identical, including the level of sunscreen, one can easily double the SPF value of an emulsion by adequate selection of the emollients. However, it is very difficult to draw general conclusions on the effect of a specific emollient as it will vary from one formulation to the next. Table II below summarizes the attributes of a few useful emollients for sunscreen formulations.

Choosing the right emulsifier and emollient(s) to achieve given skin feel characteristics is difficult, not least because there are so many choices available. Fortunately, help is at hand. A too] has been developed to help formulators to narrow the field. (5) The tool allows users to select up to three desired skin feel parameters, and suggests emollient/emulsifier combinations to meet those requirements. This gives the formulator a more manageable array of possible candidates, within which to apply other selection criteria. For example, if developing a UV protection product with organic sunscreens, one would want to use emollients that are compatible with the actives, for example (from the table below) triethylhexanoin.

Conclusions

Formulating a daily-use skin care product with UV protection is a double challenge; cosmetic elegance (feel and appearance on skin) is a primary concern, but good SPF efficacy is also required. Physical sunscreens offer major advantages for daily UV protection, but poor cosmetic elegance--specifically whitening--has limited their use in this application. A new development in Ti[O.sub.2] technology now means that physical sunscreen formulations can be developed which are elegant as well as effective. Novel emulsifier systems, and an understanding of the key properties of available emollients, enable the formulator to choose the most appropriate vehicle for the actives selected.

Formulation WI 2030-032
0/W Lotion

Ingredients                      % w/w

Phase A

Steareth-2                        3.00
Steareth-21                       2.00
Ethylhexyl stearate               9.00
Cetostearyl alcohol               1.00
Dimethicone, 5 cs                 1.00

Phase B

Demineralized water              66.60
Magnesium Aluminium Silicate      0.50
Ti02 Aqueous Dispersion          12.50
(40% solids, 30% Ti02)
Propylene glycol                  4.00

Phase C

Germaben II                       0.40

Procedure:

Disperse Veegum in water. Add
remaining phase B ingredients. Heat
phases A and B to 75[degrees]C. Add A to B
slowly with moderate stirring.
Homogenize for appropriate time.
Allow to cool with moderate stirring.
Add phase C below 40[degrees]C.

Formulation WI2030-051/1
0/W Lotion

Ingredients                % w/w

Phase A

Glyceryl stearate           2.50
  (and) PEG-100 stearate
Cetyl alcohol               2.50
Sorbitan tristearate        0.80
PEG-40 stearate             0.75
Dimethicone, 350 cs         2.00
Mineral oil                 8.00
Propylparaben               0.10

Phase B

Water                      54.90
Glycerine                   4.00
Methylparaben               0.15
Propylene glycol            4.00
Ti02 Aqueous Dispersion    15.00
  (40% solids, 30% Ti02)

Phase C

Water                       5.00
Germall 115                 0.30

Procedure:

Heat phases A and B to 80[degrees]C, with stirring
until homogeneous. Add A to B
with stirring. Homogenize for appropriate
time. Cool to room temperature
with moderate stirring (add at 40[degrees]C).

Table I: Dispersion Characteristics of Ti[0.sub.2] Materials

                                        Ti[0.sub.2]
Dispersion   % Solids   %Ti[0.sub.2]    Crystal Form

1               40           30            Rutile
2               40           30            Rutile
3               43           34           Anatase
4               40          37.4       Rutile/Anatase

Dispersion   Coating

1            Hydrophobic (alumina/aluminium stearate)
2            Hydrophilic (silica/alumina)
3            Hydrophilic (silica/alumina)
4            Hydrophobic (Trimethoxycaprylylsilane)

Table II. Attributes of Typical Emollients in Sunscreen Formulations

                                                    Organic
                                                   sunscreen
                                                 compatibility

Product          INCI Name                      Liquid   Solid

Estol 3609       Triethylhexanoin                 5       3-4
Prisorine 2021   Isopropyl isostearate           3-4       3
Prisorine 2034   Propylenc glycol isostearate     3        5
Prisorine 2039   Isostearyl isostearate           3        3
Prisorine 3505   Isostearic acid                  4        5

                                Skin
Product          Spreading   Absorption   Substantivity

Estol 3609           5           5              3
Prisorine 2021       5           5              3
Prisorine 2034       5           5              3
Prisorine 2039       5           5              5
Prisorine 3505       5           5              2

                                             Skin
Product          Moisturization   Gloss   Elasticity

Estol 3609             3            3         1
Prisorine 2021         5            3         2
Prisorine 2034         3            3         5
Prisorine 2039         2            2         2
Prisorine 3505         2            3         1

References

(1.) J.L.Robb, L.A.Simpson and D.F.Tunstall, "Scattering & Absorption of UV Radiation by Sunscreens Containing Fine Particle & Pigmentary Titanium Dioxide," Drug & Cosmetic Industry, March 1994.

(2.) J.Woodruff, "Formulating Sun Care Products with Micronised Oxides," Cosmetics & Toiletries Manufacture Worldwide (Aston Publishing Group), 1994, pp.179-185.

(3.) J.P.Hewitt, "A Moment of Clarity," Soap, Perfumery & Cosmetics, 75(3), pp.47-50, March 2002.

(4.) P.Rossi, "Bringing Food to the Soul of Your O/W Emulsion with a Dual Rheology Stabilizing System", Cosmetics & Toiletries, 116(11), pp.73-78, November 2001.

(5.) SenSelect; for more details please contact your local Uniqema representative.