variation of sunscreen efficacy using solar spectrum and solar simulators

Diapositive 1

8th Congress of the European Society for PhotobiologyGranada, Spain, 3-8 September, 1999

L’ORÉALR E C H E R C H E

SUNSCREEN EFFICACY CAN VARY WITHSUNSCREEN EFFICACY CAN VARY WITHTHE UV SOLAR SPECTRUM AND THE THE UV SOLAR SPECTRUM AND THE

STANDARD FOR UV SOLAR SIMULATORSSTANDARD FOR UV SOLAR SIMULATORS

A. Chardon, F. Christiaens, L'Oréal Recherche, Clichy (France)

&J. Dowdy, R. Sayre

Rapid Precision Testing Laboratory, Cordova TN (USA)

Ladies and Gentlemen, good afternoon!

Diapositive 2

• Sunscreen efficacy: Sun Protection Factor (SPF)• European Standard: Colipa SPF test method• Standard sun: quasi-zenithal spectrum• UV solar simulator:

– Xenon + optical filters– Criterion: spectral erythemal efficacy (RCEE)


INTRODUCTION

The Sun Protection Factor (SPF) labelled on the sunscreen products to quantify their

efficacy to protect the skin against sunburn is evaluated in human skin using a solar

simulator as an artificial source of ultraviolet rays.

The characteristics of the emission spectrum of this solar simulator are particularly

specified in the European Colipa SPF test method, in comparison with that of a

standard quasi-zenithal sun spectrum defined in the method for low earth altitude.

The solar simulator is made of a xenon source whose spectrum is modified with

appropriated short and long cut-off filters to only retain the desired ultraviolet

wavelengths in the right proportion.

This proportion is checked using as a criterion the spectral distribution of the

erythemal efficacy of the source.

Diapositive 3

• Potential variation of the SPF value, with:– Sun altitude (Air Mass)– Type of sunscreen (absorption profile, UVB / UVA) – Cut-off filters of the UV source


AIM

The aim of this modelling study is to point out the potential variation of the SPF value

of sunscreen products with the quality of the standard sun spectrum retained, as this

quality varies with the sun altitude above the horizon, that is to say with the air mass

crossed by the sun rays.

This was performed in relation with the type of sunscreen to be tested, characterised

by the UVB to UVA ratio of their absorption profile.

The effect of variation of practical cut-off optical filters used the UV source will also

be examined.

Diapositive 4

• Skin erythema action spectrum E(λ)• UV source emission spectrum S(λ)• Sunscreen absorption spectrum mPF(λ)


MEANS

∑

∑

∆

∆= nm

nm

nm

nm

mPFSE

SEspf 400

290

400

290

)(/*)(*)(

*)(*)(

λλλλ

λλλ

For this modelling study we used as a response this expression of the SPF, used in

in-vitro SPF determination and which includes:

- the CIE 1987 erythema action spectrum E(λ)

- the spectral irradiance of the UV source E(λ)

- and the monochromatic protection factor of the product mPF(λ)

The sums are integrated, nanometer by nanometer between 290 and 400

nanometers.

Diapositive 5

• CIE (1987) Erythema Action Spectrum E(λ)


1E-04

1E-03

1E-02

1E-01

1E+00

1E+01

280 300 320 340 360 380 400

Wavelength (nm)

Rel

at. R

espo

nse

(1/M

ED)

E(λ) = 1

E(λ) = 0.094 * (298 - λ)

E(λ) = 0.015 * (139 - λ)

The CIE erythema standard action spectrum with the 3 corresponding formulae.

Diapositive 6

• UV Source Emission Spectrum S(λ)


1.0E-05

2.0E-01

4.0E-01

6.0E-01

8.0E-01

1.0E+00

1.2E+00

1.4E+00

1.6E+00

290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

Rel

at. I

rrad

. (no

rm. 3

50nm

)

UG5 / 2mm

UG11 / 1mm

Colipa standard sun

WG320 /1mm

1.5mm2mm

Filtered xenon

Here are some examples of emission spectra of the UV source tested in the study.

Diapositive 7

• UV source emission spectrum characterised by theUVB (290-320nm) Relative Cumulative Erythemal Efficacy (UVB-RCEE%)


100**)(*)(

*)(*)(% 400

290

320

290

∑

∑

∆

∆=− nm

nm

nm

nm

SE

SERCEEUVB

λλλ

λλλ

The emission spectrum of the UV source, either sun or UV solar simulator, is usually

characterised by using:

the Relative Cumulative Erythemal Efficacy or RCEE percentage at various

wavelengths.

Thus, the RCEE value calculated at 320nm, giving the UVB ratio in the total

erythemal effectiveness of the UV source, is particularly significant.

Diapositive 8

• Typical UVB-RCEE % values:

– Colipa standard sun 84%– Colipa acceptance limits of the UV source:

• Upper limit• Lower limit 80.0 %

– AM 1 85 %– AM 1.5 75 %– AM 2 67 %


91.0 %

The UVB-RCEE value of the Colipa standard sun is 84%, while the lower acceptance

limit of the current method for the UV solar simulator is 80 % and the upper limit is

91 %.

This upper limit corresponds in fact to a sun spectrum of more than five thousand

meter altitude, which is not very realistic.

The UVB RCEE% of AM1.5 corresponding to a sun with 48° zenithal angle is 75%,

and that of AM2 corresponding to 60° zenithal angle is 67%.

Diapositive 9

P4SPF 15

• 4 Typical SPF15 Sunscreens: mPF Curves


1

6

11

16

21

26

31

36

280 290 300 310 320 330 340 350 360 370 380 390 400Wavelength (nm)

mPF

P1 : BP2 : B + aP2 : B + AP4 : B = A

P1

P2

P3

UVB UVA

The absorption profiles of the four products tested, based on actual filtering systems,

are represented on this graph in term of monochromatic protection factors (mPF), all

four spectra resulting in the same SPF 15 value, as calculated with the Colipa

standard sun spectrum.

Product P1 with no UVA protection added;

Product P2 with a low amount of UVA protection added;

Product P3 with a medium level of UVA protection;

and Product P4 with a rather flat profile, offering similar UVA and UVB protection.

Diapositive 10


• Global potential effect of the UVB RCEE of the UV source on SPF values of 4 typical sunscreens

• Variation between the Colipa acceptance limits• Variation of actual possible UV source filtering

systems


RESULTS

Let us now examine the results:

- the global potential effect of the UVB RCEE of the UV source on the SPF values of

each sunscreen

- the variation in the Colipa acceptance limits of source

- the effect of variation on the optical filtering system of the UV source.

Diapositive 11


Potential effect of UV source variation on SPF of Product P1

1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF15B

75

AM1AM 2 AM 1.5

6726

AM 5.6

SPF 15

84

The blue curve of this graph represents the overall potential variation of the

calculated SPF value of Product P1 (with no UVA protection added) in relation with

the UVB erythemal effectiveness of the source, ranging from high altitude sun (I

mean in high mountain) to sun at 30° above the horizon at sea level.

It is clear that the SPF value may vary considerably (from 6 to 25, for nominal value

15), the more intense the sun, the higher the calculated SPF value.

Using a UV source more effective than the standard sun would induce a significant

overestimation of the SPF value, as compared with the nominal value of 15.

Diapositive 12



1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF15B

P2: SPF15B + a

75

AM1AM 2 AM 1.5

6726

AM 5.6

SPF 15

84

Results (ctd.) (Option 1 - Three slides)

With product P2, including a minimal UVA protection added, the overall variation of

the SPF, as shown by the green curve, is already strongly reduced, as compared

with Product P1. The SPF then ranges from 8 to 20.

Diapositive 13



1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF15B

P2: SPF15B + a

P3: SPF15B + A

75

AM1AM 2 AM 1.5

6726

AM 5.6

SPF 15

84

With product P3, including a significant UVA protection added, the variation of the

SPF, as shown by the pink curve, the calculated SPF ranges from 11 to 17.

Diapositive 14



1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF15B

P2: SPF15B + a

P3: SPF15B + A

P4: SPF15B ~ A

75

AM1AM 2 AM 1.5

6726

AM 5.6

SPF 15

84

Finally, with product P4 in red, with high UVA protection and presenting a rather flat

absorption profile, the SPF value no longer varies with the quality of the emission

spectrum of the UV source. The SPF remains constant at nominal SPF15 value.

Diapositive 15


Potential effect of UV source variation on SPF of Products P1-P4

1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF15B

P2: SPF15B + a

P3: SPF15B + A

P4: SPF15B ~ A

75

AM1AM 2 AM 1.5

6726

AM 5.6

SPF 15

84

Results (Ctd.) (Option 2 - One slide)

With product P2, including a minimal UVA protection added, the overall variation of

the SPF, as shown by the green curve, is already strongly reduced, as compared

with Product P1. The SPF then ranges from 8 to 20.

With product P3, including a significant UVA protection added, the variation of the

SPF, as shown by the pink curve, the calculated SPF ranges from 11 to 17.

Finally, with product P4 in red, with high UVA protection and presenting a rather flat

absorption profile, the SPF value no longer varies with the quality of the emission

spectrum of the UV source. The SPF remains constant at nominal SPF15 value,

whatever the source.

Diapositive 16


Current Colipa UV solar simulator standard

1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF 15B

P2 : SPF 15B+a

P3 : SPF 15B + A

P4 : SPF 15B ~A

756726 84

Current COLIPA acceptance limits :

80% - 91%

AM 2 AM 1.5AM 5.6

Colipa Std Sun

SPF 14

SPF 21

SPF 15

AM 1

Now let us be more realistic:

Of course, if the artificial UV source, used for the in vivo SPF determination in human,

complies with the current specifications of the Colipa SPF test method reported on

this graph, the potential variation of the SPF of Products P1 to P3 are more limited.

However, the SPF of product P1 could still vary from 14 to 20, or to higher values like

24 with when the solar simulators exceed the Colipa standard upper limit, which may

lead to a significant overestimation of the product actual protection.

It must be noticed here that the current acceptance limits of the current Colipa

standard, though its merits, appear still too wide, with the upper limit already

exceeding the characteristics of the zenithal sun at sea level.

Diapositive 17


Proposed new acceptance limits for UV solar simulators

1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100

UVB %RCEE of the UV SOURCE

SPF

P1: SPF 15B

P2 : SPF 15B+a

P3 : SPF 15B + A

P4 : SPF 15b+A

756726 84

PROPOSEDsolar simulator

acceptance limits:75 - 84%

AM 2 AM 1.5AM 5.6 AM 1

SPF 15

SPF 13

SPF 17

For these reasons, we propose:

- firstly, to tighten the acceptance limits of the current Colipa SPF test method;

- secondly, to lower the upper acceptance limit down to the standard sun

characteristics (with 84% UVB RCEE), and the lower limit down to 75%, these limits

representing sun variation from zenith to 42° altitude above the horizon, that’s to say

from AM1 to AM 1.5, in the range where the shadow rule applies, which says that

“the risk is at maximum as long as your shadow is longer than your height” .

In these conditions, the SPF of product P1 could only vary from 13 to 17 in relation

with the artificial UV source spectrum.

Diapositive 18


Potential effect of short cut-off filter characteristics

1

6

11

16

21

26

31

0 10 20 30 40 50 60 70 80 90 100UVB %RCEE

of the UV SOURCE

SPF

P1: SPF15B

WG320 / 1mm

8475

AM 1AM 2 AM 1.5

6726

AM 5.6

+5nm +2.5nm NOM. -2.5 -5 -7nm

Now, let us speak in terms of practical filtration.

According to Schott catalogue, the cut-off wavelength at 50% transmission of WG320

filter (used for mimicking the ozone layer) may vary from - 6 to + 6nm and these

specifications have been recently changed, adding more uncertainty.

Fortunately, the typical actual variation observed is much lower.

However, this means that the characteristics of the filter batch must be carefully

checked and the thickness of the filter adapted accordingly, following the procedure

recommended by the Colipa SPF test method.

Diapositive 19


Potential effect of long w.l. filtration: UG5 / 2mm - UG11 / 1mm

1

6

11

16

21

26

0 10 20 30 40 50 60 70 80 90 100

UVB %RCEEof the UV SOURCE

SPF

P1: SPF15B

P4 : SPF15B = A

UG11 / 1mm

UG5 / 2mm

UG11 / 1mm

UG5 / 2mm

8475

AM 1AM 2 AM 1.5

6726

AM 5.6

As far as the long cut-off filtration is concerned, this graph shows the potential SPF

variation obtained when changing from a Schott UG5 2mm filter to a UG11 - 1 mm

thick.

The change would be minor for the flat product P4.

For product P1, the change could be more significant, inducing a difference of about

1 SPF unit and the nominal value would be better approached with the UG5 filter.

Diapositive 20

CONCLUSION: Sunscreen SPF can vary with the UV source spectrum

• SPF increases when the source spectrum shows:– more short UVB– less long UVA

• Colipa SPF test method should recommend spectrum limits leading to more accurate SPF values

• SPF of highly UVA protective sunscreens do not depend on UV source conditions


Conclusion (option 1)

As a conclusion, this modelling study shows that:

- the sunscreen SPF increases when the UV source spectrum contains more UVB

energy

- or less long UVA energy than the standard sun.

The UV solar simulator acceptance limits of the current Colipa SPF test method

should be tightened and lowered so that the conditions of the zenithal standard sun

could not be exceeded in order to yield more realistic SPF values.

The SPF of highly UVA protective sunscreens do not depend on the quality of the UV

source spectrum.

Thank you very much for your attention.

Diapositive 21

• SPF tends to increase when more short UVB are present in source spectrum (increasing UVB-RCEE%)

• SPF tends to slightly increase when less long UVA are present (with UG11 filter)

• Higher UVA protection in product leads to: – lower SPF variation with short (WG320) or long (UG)

wavelength variationL’ORÉALR E C H E R C H E

CONCLUSION 1

Conclusion (option 2):

In conclusion, this study showed that:

-The SPF of the products tends increasing when relatively more UVB are present in

the source spectrum, that’s to say when the UVB RCEE increases.

-The SPF tends to slightly increase when less long UVA are present in the source

spectrum, (I mean with UG11 filter instead of UG5.)

-Increasing the UVA protection in the products allows reducing all these effects on

the SPF values.

Diapositive 22

• Increasing labelled SPF values call for:– Better control of the UV source spectrum– More realistic UV spectrum– Lower and tightened Colipa acceptance limits:

• Upper acceptance limit ≤ AM 1 standard sun• Lower acceptance limit ~ AM 1.5


CONCLUSION 2

Because of increasing labelled SPF values, there is a need for

- a better control of the UV source spectrum

- a more realistic UV spectrum, which means that the Colipa acceptance limits should

be tightened and lowered so that the conditions of the zenithal sun (AM 1) could not

be exceeded.

Standardising the long cut-off filtration by recommending the UG11 filter would allow

to reduce the heat load on the skin and on the products, while further reducing the

SPF variation.

Diapositive 23

• Reducing the UVB RCEE% of the source:– would reduce erythemal effectiveness of the UV source– would increase MED irradiation times

• Compensated by more powerful UV sources available


CONCLUSION 3

On a practical point of view and as a consequence, reducing the UVB RCEE of the

UV source would likely reduce its global erythemal effectiveness, while increasing the

UV exposures accordingly.

But this can be compensated with the more powerful UV sources available.

Tank you very much for your attention !

Diapositive 24



Photo A.Chardon

variation of sunscreen efficacy using solar spectrum and solar simulators

Technology