Sunscreen testing: ISO implications for ASEAN

A third document – ISO 244433 – in vitro UVA – (UVAPF) is in its final draft stage, with technical changes now locked in and only final editing to be completed. Adoption of these documents will no doubt impact on the development of sunscreen products in ASEAN member countries, particularly where the intention is to export these to other parts of the world. ISO methods should be accepted as equivalent to COLIPA, JCIA or EU protocols and do offer the potential for eventual acceptance in many other markets. This is in keeping with the objective harmonisation recognised by the participant countries involved in the development process.

SPF test – in vivo

Essentially, changes to the Sun Protection Factor test method are fairly minor and should not require retesting on the basis of SPF claim support. The harmonisation takes into account the protocols currently in existence in EU, China, Korea, Australia, New Zealand, FDA and Canada.4 Set out in Table 1 is the comparison of COLIPA and ISO test parameters. As can be seen, these two methods are almost identical in respect of the important experimental parameters.

UVA – PPD Testing

The in vivo method finalised by ISO is very much in line with the JCIA method long accepted in Japan. In COLIPA countries, this is an alternative to in vitro testing and there is sufficient evidence to support the equivalence of in vitro with in vivo. However, for those markets where it is mandatory to test according to an in vivo method, the harmonised ISO method is equivalent to JCIA and should be acceptable in all markets where regulations mandate only this in vivo UVA test. The significant differences are, firstly, the allowance for a broader time delay from UVA exposure and reading of the Persistent Pigment Darkening (PPD) response. This is now 2 to 24 hours, allowing for the requirements of both FDA and JCIA. Other additions are more quality control requirements for the reference sunscreen, allowance for 10 to 20 test subjects and reviewed requirements for the calibration of the Xenon arc light source. These changes have a positive impact on the test methodology, making the protocol truly harmonised and it should be acceptable to authorities in those markets, subject to regulation.

UVAPF in vitro testing

Following the finalisation of technical drafting of the ISO test method for in vitro UVA (broad spectrum) testing, COLIPA have published, in March 2011, an updated version of the corresponding document for the EU. This guideline, “Method for the in vitro determination of UVA protection, 2011”, is basically aligned with what is currently proposed as ISO 24443 – “Determination of Sunscreen UVA photoprotection in vitro”. The latter document has now reached the stage of Final Draft International Standard. Adoption for Australia as the revised test method for support of the “Broad Spectrum” claim for sunscreens is now likely to be March to June 2012. A summary of the differences between the previous COLIPA method, the new COLIPA and ISO (as expected, but subject to final change) is set out in Table 2. The COLIPA method varies significantly and could give different results when compared with measurements made using the previous version. Testing which is conducted to the new COLIPA version should be valid for ISO – Australian – New Zealand purposes. The more significant changes are as follows: Substrate The substrate has been standardised to Polymethyl Methacrylate (PMMA) with a roughness profile specified. Previously, this was 2 micron, but is now 6 micron.

Application rate

Change to the substrate roughness now allows for a thicker film to be applied – 1.3 mg/cm2 compared with 0.75 mg/cm2 previously specified. This film thickness change will impact on the ratios measured for some sunscreens, particularly when they contain inorganics.

Drying time

 Allowance for the drying down of the thin film, once it has been applied and spread onto the PMMA plate substrate, can provide variation in measurement. Most significantly, if the film continues to dry down while it is at the next test stage – pre-irradiation under UV light – then this can result in exaggerated changes which are not related to photo instability, but may be interpreted as such. ISO will be more generous in this provision.

SPF used for pre-irradiation challenge

This is consistent between the proposed ISO and COLIPA, with the intent that the in vivo SPF is used for the light challenge. Products with a high SPF or formulated for longer water resistance, can appear to be disadvantaged.

SPF used for calculation of final claimed UVAPF ratio

The wording of this in the COLIPA document is still a little confusing, but what is interpreted is that the calculation of the ratio is made against the label claim SPF.

Validations and calibrations The working group of ISO considered, in some detail, the requirements for consistency of measurement between laboratories. As a result of this, a number of calibration requirements have been incorporated and these are now reflected in the new COLIPA version.

•  A Reference Sunscreen is used in order to confirm the product application technique of the technician.
•  The pre-irradiation instrument, typically a solar simulation light source, must be calibrated at specified intervals and comply with spectral, flux and heat limits.
•  The measurement instrument used for determination of the quality and quantity of the spectra produced pre and post the UV light challenge, must be calibrated monthly for linearity, wavelength accuracy and sensitivity.

Compliance

For EU compliance, the COLIPA requirements are for the sunscreen to achieve a UVAPF ratio of one third of SPF. As well, a critical wavelength of at least 370 nm must be obtained. As it is to be purely a test method, ISO will not require any minimal performance limits. Interpretation of the measurements is left to the regulatory environment of the geographical market. For compliance in Australia, the UVAPF Ratio of one third of SPF will need to be achieved. The definition of “SPF” for this purpose is yet to be decided.

Other methods under development

In vivo SPF

Progress in development of this is still slow and complex, but the creative talent of the international expert participants has generated some interesting approaches. Recently and independently, there has been considerable experimentation in the areas of:

• Goniospectrophotometric measurements (Germany).
• In silico modelling of in vitro SPF prediction (Germany).
• Rheology of sunscreen formulations (Monaco).
• Effect of training in film presentation technique (France).
• Effect of sample application pressure (Japan).
• Effect of chemical pre-treatment of the substrate (France).
• Effect of physical pre-treatment of the substrate (France).

The progress and potential of these test parameters will be reviewed and composited into an inter-laboratory ring study later this year.

Water resistance?

This “missing part” of this ISO sunscreen series has advanced to its 3rd version. In line with other ISO standards, it is restricted to a test methodology, without incorporating any performance requirements – such as pass/fail or definitions. It is essentially a water immersion test method. With many of the parameters for this now agreed, the drafting has advanced sufficiently for a ring test to be initiated, mainly to focus on and refine the specification of issues such as the water flow and spa shape variance between pools currently in use in test centres. At least 10 laboratories will collaborate in the study. The outcome of the ring study is scheduled to be reported to the November 2011 ISO plenary meeting.

John Staton is director of Dermatest Pty Ltd, Australia. He is currently lead delegate from Standards Australia to ISO Technical Committee 217 Working Group 7 – Sunscreens.

References

1 ISO 24444 – Cosmetics – Sun Protection Test Methods – in vivo determination of sunscreen UVA protection. Version Final, Nov 2010. 2 ISO 24442 – Cosmetics – Sun Protection Test Methods – in vivo determination of sunscreen UVA protection. Version DIS 24442, May 2010. 3 ISO 24443 – Cosmetics – Sun Protection Test Methods – determination of sunscreen UVA photoprotection in vitro. Version FDIS, April 2011. 4 ISO DTR 26369 – Cosmetics – Sun Protection Test Methods – Review and evaluation of methods to assess the photoprotection of sun protection products. Version May 2008.