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Reprint

from

7-2005

International Journal

for Applied Science

■ Personal Care ■ Detergents ■ Specialities

K. Berg-Schultz, Ch. Mendrok, F. Sit, R. Jermann:

Formulating High SPF Sun Care Products

with a Liquid-Mineral UV Filter


SUN CARE

LIQUID-MINERAL UV FILTER

K. Berg-Schultz, Ch. Mendrok, F. Sit, R. Jermann*

Formulating High SPF Sun Care Products

with a Liquid-Mineral UV Filter

Keywords: Sun Care, Polysilicone UV Filter, High SPF Formulation, Enhanced Sensorial Profile

� Introduction

Abstract

The novel architecture of the

new UVB filter, PARSOL ® SLX

(INCI: Polysilicone-15) combines

the desirable attributes of

both polydimethylsiloxane and organic

UV filters. It exploits the

film-forming characteristics of

polydimethylsiloxanes on human

skin, ensuring an optimal distribution

of the attached UV absorbers

when applied as a sun cream.

This results in remarkably high

performance sun care products

which are suitable for all skin

types but especially for sensitive

skin due to its minimal skin penetration.

Formulated products containing

Polysilicone-15 also convey

appealing sensorial aspects

while remaining easy to use and

handle.

Due to the increased awareness of consumers

that excessive sun exposure can

lead to damages such as premature skin

aging, sunburn, immune suppression, and

different types of skin cancer (1,2) the

consumption of sun care products has

steadily increased in the last decades. Simultaneously,

the sun protection factor

(SPF) of products found in the marketplace

increased significantly. Whereas,

10 years ago an SPF of 4 to 20 was the

common practice, today usual sun care

products exhibit SPF’s of 20 up to SPF’s

of 50+.

For formulators the preparation of a

sunscreen having a SPF of 40 or more is

still a challenging task and needs a lot of

experience and skills, especially as it is

well known that an increase of the UVfilter

concentration does not steadily

lead to a higher SPF. Thus, in order to

achieve a high SPF different UV-filters

have to be combined (Fig. 1) (3). Nevertheless,

not all UV-filter combinations

lead to expected higher SPF’s and often

several trials of different combinations

are necessary (4).

In a sun care product with a high SPF, the

UV-filters represent an important proportion

of the total formulation and

SPF

filter 1+2+3

filter 1+2

Fig. 1 Synergistic effect of UV filter

combinations in cosmetic formulations

therefore contribute significantly to the

sensory profile of the product. However,

high levels of traditional organic sun filters

can lead to aesthetically unpleasing

effects with regard to greasiness and

tackiness of the formulation. On the other

hand inorganic UV-filters such as minerals

and pigments have an undesirable

residual whitening effect on the skin

which makes the skin look pale (Fig. 2).

Fig. 2 Whitening effect on the skin

As the consumers dislike such features

the choice and combination of UV-filters

used in sunscreen formulations is crucial.

Additionally, photo-stability, safety aspects,

easy handling in production, product

stability and costs have to be taken

into account in the development of a

sunscreen product. For this reason, the

cosmetic industry desires UV-filters which

provide effective protection against UV

radiation reflected by a remarkable SPF

performance, which are easy to formulate

and have a pleasant skin feel.

2 SÖFW-Journal | 131 | 7-2005

filter 1

UV-filter concentration


� Polysilicone-15 –

a liquid mineral UV-filter

Polysilicone-15 is the first commercial

example of a completely new generation

of UV filters which were specifically designed

to meet the needs of the cosmetic

industry. Unlike conventional monomeric

UV filters, this innovative UV filter constitutes

a hybrid of silicone technology

and classic organic UV-filter chemistry. A

closer look at the structure of the molecule

reveals, that the mineral silica in

form of a polysiloxane chain serves as

polymeric backbone for the chromophore

units (Fig. 3).

This combination leads to a unique polymeric

UV filter which besides being liquid

at all temperatures has excellent cosmetic

properties and minimizes the risk

of skin penetration due to its high molecular

weight of about 6000g/mol. Although

the polymeric backbone represents

more than 70% of the molecular

mass and does not contribute to the UV

absorption as reflected by a low UV specific

extinction (E 1%, 1cm), Polysilicone-

15 delivers in vivo SPF performance comparable

with industry standards, such as

Ethylhexyl Methoxycinnamate (EHMC)

(Fig. 4). This, at first sight, surprising result,

can be explained by looking into

the behavior of different UV-filters on

the skin.

� In vivo performance of

Polysilicone-15 versus EHMC

How can it be, that a molecule, which has

less than 30% of its molecular weight

contributing to sun protection, obtains

the same SPF performance as the benchmark

molecule EHMC? An explanation of

this question needs some insight into the

behavior of sun-filters in general and of

their behavior on the skin.

Numerous attempts have been made to

understand how sunscreen preparations

protect against UV radiation (5-9). Up to

now the measurements of the sun protection

factor (SPF) of emulsions containing

traditional UV absorbers clearly

indicated that the efficacy depends on

the absorption characteristics of each single

UV filter substance. However, it is also

well accepted that the Lambert Beer’s Law

is not obeyed at high concentrations

SUN CARE

LIQUID-MINERAL UV FILTER

Fig. 3 Structure of Polysilicone-15

Fig. 4 In vivo SPF comparison of Polysilicone-15 and EHMC

(>0.01M) as present in sunscreen formulation

due to electrostatic interactions

between molecules in close proximity. At

high UV absorber concentrations, as commonly

found in sunscreen formulations,

this leads to a drop of the UV absorption

properties and consequently to a loss of

the theoretical protection abilities. Additionally,

the degree of UV absorption

achieved by the UV filters within a sunscreen

formulation depends on the irregularities

in the geometry of the sunscreen

film after application on the skin

(5, 8-12). Reason for the uneven distribution

of UV-filters on the skin are manifold

and can be caused besides the rough-

ness of the skin due to wrinkles, cracks,

hair and gland shafts, by aggregation of

the aromatic UV filter molecules due to

π-π interactions (13,14) or agglomeration

of nanopigments as well as by microcrystallisation

of an ingredient on the

skin (15).

Various models have been proposed in

order to predict the in vivo SPF which are

based on the Lambert Beer’s Law and

which take the film irregularities into account.

In 1983 O’Neill (12) proposed a

simple model of irregular film, a step film

geometry, which satisfactorily account

for the discrepancy between measured in

vivo data and simple spectroscopic data.

SÖFW-Journal | 131 | 7-2005 3


SUN CARE

LIQUID-MINERAL UV FILTER

This purely mathematical model shows

that the transmission properties of a homogenous

film decreases significantly

with increasing film irregularities represented

by the step film parameters f and

g and can be calculated as the sum of the

transmissions through the two fractions

of the film (Fig. 5).

Herzog et al. (10,11) refined this simple

model by correlation of calculated data

with measured in vivo SPF data and

hereby defining the parameters f and g

to be g = 0.269 and f = 0.935. These values

reflect a considerable roughness of a

sunscreen film as visualized in Fig. 6.

Using these parameters they have a

calibrated tool at their hands, called ‘the

sunscreen simulator’ (16). This tool allows

a good prediction of in vivo SPF’s

for a given roughness of the film and

in dependency of the UV-filter concentration

(Table 1, B1-B3). However, this

method fails in the prediction of the in vivo

performance for formulations containing

Polysilicone-15 (Table 1, A1-A3).

This result is not surprising as Polysilicone-15

has a comparable low UV specific

extinction. Nevertheless, there are

other effects compensating the low UV

specific extinction which can be explained

using the same mathematical

model based on the step film theory. Traditional

organic UV-filters as well as inorganic

or organic pigments are concentrated

on the skin surface after application

and evaporation of the water phase.

During this concentration process, traditional

organic UV-filters tend to aggregate

(13) as well as pigments tend to agglomerate.

Due to these reasons, it is difficult

to distribute the UV-filters evenly

over the inherently rough skin surface.

The model proposed by Herzog (16) using

formulation containing traditional

UV filters takes these effects into account

through the choice of the parameters

f and g. However, this model does

not consider effects which lead to a more

even distribution of the UV-light absorbing

units on the skin which would

consecutively be reflected in higher values

for g and lower values for f.

Through the unique structure of Polysilicone-15

the aggregation of the chromophoric

systems is significantly reduced.

This is the case as the chromophore units

are hold apart by the dimethylsiloxy-

Fig. 5 The step film model as introduced by O´Neill (12)

Fig. 6 The calibrated step film model by Herzog et al (10,11,16) reflecting

in vivo conditions

INCI A1 B1 A2 B2 A3 B3

Polysilicone-15

Ethylhexyl

PARSOL® SLX 5 3 3

Methoxycinnamate

Butyl Methoxy-

PARSOL® MCX 5 3 3

dibenzoymethane

Phenylbenzimidazol

PARSOL® 1789 2 2 2.5 2.5

Sulfonic Acid

4-Methylbenzylidene

PARSOL® HS 2 2 2 2

Campher PARSOL® 5000 3 3 4 4

Titanium dioxide Uvinul® TiO2 4 4

Calculated in vivo SPF according to (16) 4 7 14 20 33 44

Measured in vivo SPF* 10 11 20 21 44 41

*International Sun Protection Factor (SPF) Test Method, COLIPA, February 2003

Table 1 The ‘sunscreen simulator’

4 SÖFW-Journal | 131 | 7-2005


uilding blocks leading to a defined distance

between the chromophores. The

average ratio of the dimethylsiloxy-units

to the chromophore carrying silicone

units is about 15 to 1 at an average chain

length of 64 (Fig. 3). Thus, every chromophore

unit in Polysilicone-15 contributes

more effectively to the sun protection

activity. Furthermore, due to a

low surface activity which is generally

found in silicone oils as e.g. described for

polydimethylsiloxanes in (17,18), Polysilicone-15

has due to its molecular structure

excellent spreading and film forming

abilities. Therefore, polysilicone-15

is able to smoothen the roughness of

the film leading to a significantly increased

protection despite the low UV

specific extinction. For these reasons,

Polysilicone-15 at equal concentrations

compared to EHMC gives similar in vivo

SPF’s.

� Polysilicone-15 in combination

with other UV-filters

As explained in the beginning, UV-filters

are normally combined to reach a cost

effective SPF. The Tables 2 and 3 shows

the advantages but also limits of Polysili

cone-15 in combination with other UVfilters.

All formulations used are basic oil

in water emulsions and contain the UVAfilter

Butyl Methoxydibenzoyl Methane

(BMDBM). An exemplary O/W formulation

is shown in Table 4.

Replacement of EHMC by

Polysilicone-15

For sun care products, where safety is

very important and it is desirable to replace

EHMC by another UVB-filter, Polysilicone-15

is a potent and safe alternative.

Table 1 shows the in vivo SPF comparison

of formulations containing either

3% EHMC or 3% Polysilicone-15. It

has been shown, that similar in vivo SPFs

can be obtained.

Synergistic effect of Polysilicone-15

with other UV-filters

Combinations of Polysilicone-15 with existing

UV-filters show synergistic effects

on the in vivo SPF as can be seen in Table 2.

SUN CARE

LIQUID-MINERAL UV FILTER

INCI A B C D

Polysilicone-15 PARSOL® SLX 3 3

Butyl Methoxydibenzoymethane PARSOL® 1789 2.5 2.5 4 4

Phenylbenzimidazol Sulfonic Acid PARSOL® HS 2 2 4 4

4-Methylbenzylidene Campher PARSOL® 5000 4 4

Titanium dioxide Uvinul® TiO2 3 3

Measured in vivo SPF* 18 30 38 53

*International Sun Protection Factor (SPF) Test Method, COLIPA, February 2003

Table 2 High SPF formulation with polysilicone-15

INCI A1 B1

Polysilicone-15 PARSOL® SLX 3 3

Ethylhexyl Methoxydibenzoymethane PARSOL® MCX 3

Butyl Methoxydibenzoymethane PARSOL® 1789 2.5 2.5

Phenylbenzimidazol Sulfonic Acid PARSOL® HS 2 2

4-Methylbenzylidene Campher PARSOL® 5000 4 4

Measured in vivo SPF* 30 25

*International Sun Protection Factor (SPF) Test Method, COLIPA, February 2003

Table 3 Unfavorable interaction between polysilicone-15 and EHMC

INCI A B

Phase A Polysilicone-15 PARSOL® SLX 0 3

4-Methylbenylidene Camphor PARSOL® 5000 4 4

Butyl Methoxydibenzoylmethane PARSOL® 1789 2.5 2.5

Octocrylene PARSOL® 340 2 2

Hydrogenated Coco-Glycerides 3 3

Cetearyl Alcohol 2 2

Caprylic/Capric Triglyceride 21 21

BHT 0.05 0.05

preservative qs. qs.

Potassium Cetyl Phosphate AMPHISOL® K 2 2

Phase B Aqua qs. qs.

Titanium Dioxide 6 3

Butylene Glycol

Acrylates/C10-30 Alkyl Acrylate

5 5

Crosspolymer 0.3 0.3

Disodium EDTA 0.1 0.1

Phase C Aqua qs. qs.

Phenylbenzimidazole Sulfonic Acid PARSOL® HS 2 2

Tromethamine 2 2

Table 4 Standard O/W emulsion

SÖFW-Journal | 131 | 7-2005 5


SUN CARE

LIQUID-MINERAL UV FILTER

The inclusion of 3% Polysilicone-15 raises

the SPF from 18 to 30 (A and B) and

from 38 to 53 (C and D). This data are in

line with many other experiments where

it was found, that Polysilicone-15 exerts

synergistic effects when combined with

4-Methylbenzylidene Camphor (MBC),

Phenylbenzimidazol Sulfonic Acid (PBSA)

(19), Titanium Dioxide (TiO2). A possible explanation for these synergistic

effects can be found

1. In the film forming properties of Polysilicone-15

2. Reduction of the aggregation of the

traditional UV-filters

3. Reduction of the agglomeration of

pigments

and thus supporting a better distribution

of traditional UV-filters on the skin surface

(Fig. 7).

Thus, Polysilicone-15 can be used to exploit

more efficiently the UV-absorbing

potential of the traditional UV-filters.

Low performance of Polysilicone-15

in combination with EHMC

Table 3 shows the unexpectedly low in

vivo SPF results if EHMC is combined

with Polysilicone-15. If EHMC is added

to a standard sun care formulation with

SPF 30 containing 3.0% Polysilicone-15

the in vivo SPF decreased to 25. This initially

surprising result can be caused by

significant π-π interactions of the aromatic

chromophoric systems (14). This interactions

result from the similar structural

features of the benzalmalonate chromophore

and the EHMC chromophore

leading to a energetically favored aggregation.

As is known and has been discussed

above, these interactions reduce

the sun protection activity. Thus, it is not

recommended to combine Polysilicone-

15 with EHMC.

� Further unique characteristics

of Polysilicone-15

With the structure of Polysilicone-15 given,

some unique characteristics are implied

which can not be found with other

UV-filters, and which give additional

benefits for the products and the consumers.

Improved Sensorial Profile

Having a polysiloxane backbone in the

molecule, Polysilicone-15 exerts a silicone-like

feeling when applied on the

skin, especially compared to traditional

mineral UV-filters. This new technology

UV-filter shows specific advantages in

the sensorial profile and the reduced

residual whitening of the skin. To prove

this advantages two similar sun care formulations

were created (composition see

Table 4). Formulation A contained 6%

TiO 2 . In formulation B 3% of the TiO 2 was

replaced by 3% Polysilicone-15. Both

formulation achieved a comparable SPF

of 27 (A), respectively 28 (B). The replacement

of TiO 2 by Polysilicone-15 had

a considerable influence on the sensorial

profile. The two formulations were analyzed

at an external test institute where

12 trained panellists quantified the sen-

sorial profile of both formulations. Fig. 8

shows the parameters where the most

important differences were measured. It

can be seen that the speed of absorption,

the coolness, the melting and the ease of

spreading were almost all significantly

better for the formulation containing

Polysilicone-15. The whitening during and

after spreading was significantly reduced

when 3% TiO 2 was replaced by 3% Polysilicone-15.

The formulation containing

Polysilicone-15 exerts the same protection

of the skin as TiO 2 , but provides a

formulation with a much better sensorial

profile.

Increased consumer protection

The same two formulations as described

above were used for the following consumer

test at an external test institute:

Fig. 7 Synergistic effect of Polysilicone-15 in combination with other UV-filter

Fig. 8 Sensorial test: Comparison of application characteristics of a sun care

formulation with and without 3% Polysilicone-15

score

14

6 SÖFW-Journal | 131 | 7-2005


15 female volunteers in the age of 19-

52 years applied during two weeks under

normal conditions twice daily each

of the two formulations on either arm.

At the end of the application period, the

remaining product was collected and

the amount of product used was measured.

This consumer test showed that in

the average the volunteers used 29%

more of the formulation, which contained

Polysilicone-15. This means that

the consumer is much better protected

because the amount of sun filter on the

skin is almost 30% higher if Polysilicone-

15 is included in the sun care product

(Fig. 9).

Photo-stabilisation of BMDBM

To achieve broadspectrum UV protection,

Polysilicone-15 and Butyl Methoxydibenzoyl

Methane are perfect partners.

BMDBM was the first globally approved

UVA filter and has been on the market in

Europe for more than 15 years. However,

BMDBM needs to be photo-stabilised

as the molecule itself tends to photodegrade

upon irradiation.

Even though every UV-filter, purely by its

UV-light absorbing properties, stabilizes

BMDBM to a certain extent, an efficient

stabilisation can only be achieved by the

addition of a suitable triplet quencher.

BMDBM has a triplet energy of 59,5 kcal/

mol (20) and hence a suitable quencher

for BMDBM should have a triplet energy

in the order of 55-60 kcal/mol. Although

many organic molecules fulfill this requirement,

not all have a regulatory status

allowing their use in cosmetic preparations,

nor do they have a photostability

per se sufficient for this purpose. Next

to 4-Methylbenzylidene Champhor and

Octocrylene, two well established photostabiliser

for BMDBM (21,22), Polysilicone-15

with a triplet energy of 57.9 kJ/

mol acts as efficient photostabilisator

for BMDBM. The chromophoric unit, responsible

for the triplet quenching properties

of the Polysilicone-15 has the possibility

to dissipate the accepted energy

via an E/Z isomerization. Fig. 10 shows

the behavior of BMDBM at different concentrations

of Polysilicone-15. Note that

the stabilizing effect is not a question of

a defined ratio as would be expected if

it were a filter effect.

SUN CARE

LIQUID-MINERAL UV FILTER

Outstanding safety profile

The architecture of Polysilicone-15 ensures

that the molecule stays on the surface

of the skin to absorb the harmful

UVB radiation. Skin penetration studies

performed under the European SCCNFP

guidelines and GLP conditions showed

maximum retention on the skin surface

(23). Polysilicone-15 alone or in combination

with other macromolecular sun

filters (pigments or minerals) form a perfect

shield against UVB radiation for day

care products, for sensitive or damaged

skin, or for products intended for baby

and children care.


Easy to use

Being a liquid-mineral UV-filter enables

Polysilicone-15 to be easily formulated

into almost any cosmetic product without

the risk of crystallisation. Furthermore,

the molecule is stable even at harsh

conditions up to pH 9. Table 5 shows the

main properties of Polysilicone-15 which

are relevant for the formulator when

handling the product.

The broad stability and usability of Polysilicone-15

enables the formulator to

utilize it in various product forms for different

applications, such as high SPF sun

protection products, sun protection and

Fig. 9 Consumer test: Comparison of amount of product applied between a sun care

formulations with and without 3% Polysilicone-15

Fig. 10 Stabilization of BMDBM by Polysilicone-15 in a cosmetic emulsion

SÖFW-Journal | 131 | 7-2005 7


SUN CARE

LIQUID-MINERAL UV FILTER

PARSOL® SLX:

• liquid at all temperature

• stable in the pH range of 4 - 9

• stable up to 80°C for 6 hours without any loss on activity

• compatible with a wide range of organic and inorganic UV filters, common

emollients and emulsifiers

• can be formulated into O/W-, W/O- and Si/W-emulsions as well as in translucent

gels, shampoos or sprays

• no undesirable effects such as odour, discoloration, etc.

• approved in Europe at a maximum use concentration of 10% as well as in

People’s Republic of China, Taiwan, Latin America and selected Asian countries

Table 5 PARSOL® SLX – robust and easy to use

daily protection for sensitive and damaged

skin, baby and children care products

with safe sun protection or as »technical

UV-filter« in specific decorative cosmetics

(e.g. pressed powders). Additionally, Polysilicone-15

has been shown to have excellent

hair protecting properties against

UV radiation as described in (24-26).

� Conclusion

Polysilicone-15 (PARSOL® SLX) represents

a new generation of UV filters coined

»Liquid-Mineral UV Filter« by DSM Nutritional

Products, providing optimal distribution

of the chromophores on the

skin. It is an ideal complementary UVfilter,

enhancing SPF values when used

with other UV-filters in high SPF formulations.

Polysilicone-15 has excellent skin feel

and positively influences the sensorial

characteristics of a sun care product. It

also enhances the amount of sunscreen

applied on the skin and provides thus a

better protection against UV-irradiation

for the end consumers.

Because Polysilicone-15 remains on the

skin surface, it has an outstanding safety

profile. It is easy to formulate and suitable

for a broad range of high SPF and

photo-stable sun care products.

References

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Author’s addresses:

* Katja Berg-Schultz, Christine Mendrok,

Fintan Sit, Roland Jermann

DSM Nutritional Products Ltd.

PO Box 3255

4002 Basel

Switzerland

Correspondence:

Email: roland.jermann@dsm.com

8 SÖFW-Journal | 131 | 7-2005

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