Preface

Revisiting the Broad Spectrum evaluation of sunscreens has been protracted, not least because of a cycle of proposition and refutation or rebuttal which has been repeating itself now for some years and it has not proved progressive for the issue at hand.

Broadly, two positions are on the table, which I think can be readily simplified:

1. Protection from UVA needs to be addressed in itself, as if it were a discreet entity (separate from UVB) and which presents short and long term hazards to human health.

This position is represented by the German DIN, and COLIPA methods which involve the in vivo and in vitro SPF; the action spectrum for Permanent Pigment Darkening, and the UVA Ratio.  A biological endpoint(s) considered relevant to UVA alone is necessary to this approach.

2. UVA is a part of the sunlight we are exposed to and it is too much UV and not UVA apart from UVB which presents the hazard (as does too little). The Broad Spectrum  protective capability of a sunscreen can and should, together with the SPF, address this total UV spectrum (quality and quantity). 

This position is represented by the UVA Ratio alone. 
___________________ 
If we hold the first position then we must have a protection factor of some kind specific for UVA. If we hold the second position then we measure the extent to which the sunscreen protects from all wavelengths equally (and approximates clothing), and for which no protection factor is necessary.  SPF addresses quantity, and UVA Ratio addresses quality, in a complementary way.

__________________

Broad Spectrum Evaluation of Sunscreens.
Ten (10) points supporting the in vitro UVA  Ratio approach 

1. The Broad Spectrum issue results from a concern that sunscreens have tended to protect preferentially from UVB.  The UVA Ratio approach directly addresses this concern in a relatively simple, useful and easily communicable way.
 
2. No Broad Spectrum (BS) issue is raised with regard to clothing yet they are given prior rank as a sun protection modality.  This is because in general clothing protects from all wavelengths equally. 

There is a Broad Spectrum issue with sunscreens, because in general they tend not to protect from all wavelengths equally.

The UVA Ratio approach evaluates the ability of a sunscreen to protect from all wavelengths  equally. 

3. The primary reason for revisiting the Broad Spectrum part of the Standard  is because the current rationale and methods lack meaning. 

Any proposed method must therefore be justified by an obvious improvement in meaning which must also be easily communicable to the public and confer a real benefit.

The UVA Ratio method addresses the Broad Spectrum capability of a sunscreen literally. It tells us to what extent a sunscreen will change the spectrum of sunlight passing through it.  The closer the ratio approximates 1.0 or unity, the closer the sunscreen approximates a neutral density filter, and the less it changes the actual sunlight spectrum at the time of exposure. 

4. The skin hazards associated with sun exposure are not associated with sunlight itself, but with too much of it. 

It is now widely accepted that having too little sunlight can lead to health problems.  Associated mainly with vitamin D deficiencies.

The sunlight spectrum is continuous and the divisions into UVB, UVA etc are somewhat arbitrary and continue to be misleading with regard for example to the interpretation of SPF as a measure of UVB protection which it is not since solar simulators used in testing emit wavelengths with a similar power density as sunlight up to 370 nm.

A sunburn erythema induced by UVB alone is not the same as an erythema induced by UVA alone.  Different chromophores and lesions apply.  A limitation of action spectra is that they assume that the biological effectiveness at any single wavelength is independent of the effectiveness of other wavelengths.  Not only is it improbable that wavelength interactions do not occur but an increasing body of evidence suggests that they do, and are important.

Attempting to address UVA on its own reinforces the false perception that it is a discrete entity and may somehow act independently of UVB. 

The UVA Ratio approach addresses the UV region of the sunlight spectrum as a whole.

[It has been strenuously argued that adopting the UVA Ratio will encourage formulators and manufacturers to reduce the UVB protective capability to improve the Ratio.  It can be argued equally that the UVA Ratio will encourage innovation, and  is in fact a more likely choice given the impact on performance of taking the former course.]

5. The UVA Ratio addresses a physical characteristic of a sunscreen as this will apply to any and every biological consequence of UV transmission.  In other words, the UVA Ratio approach is independent of any biological endpoint. Yet it is relevant to all biological endpoints.

This independence is important because we know that skin cancer (SCC) in animal models at least is not dependent upon prior sunburn.

This independence is also important because it leaves actual biological effectiveness, as this is a function of widely varying exposure conditions, out of its equation.

Any kind of protection factor approach for UVA alone will demand a biological endpoint.  Since the meaning of any such endpoint will have questionable relevance to long term effects and be subject in vitro to the limitations shared by action spectra. 

[A good in-vivo/in-vitro correlation has been shown using the PPD action spectrum and a corrected in vitro transmission/absorbance analysis (Gers-Barlag).  However, since the in vivo exposure must leave out wavelengths > 370 nm due to the necessary filtering of the xenon arc light sources this correlation also demonstrates a radical insufficiency of this endpoint.  The SPF and erythema endpoint already takes into account UVA contributions up to 370 nm and the 63% of total solar irradiance between 370 – 400 nm which is filtered out is clearly not relevant to PPD but may be relevant to the more significant biological endpoints such as skin cancer.  Adopting a protection factor approach with in vivo data as its measure leaves out a significant portion of the very thing it attempts to measure.]  

6. Biological effectiveness is inversely proportional to wavelength, whereas skin penetration is proportional , as these are directly related.  The importance of the shorter (UVB) wavelengths for sunburn is not lessened by the  UVA Ratio which  measures an aspect of the sunscreen and makes only one assumption with respect to biological effectiveness.

The assumption which the UVA Ratio approach makes is that sunlight is okay, that if a sunscreen changes  only the quantity and not the quality of sunlight passing through it then our concern regarding the sunscreen itself and disproportionate exposure to UVA is relieved of a long standing emphasis.

7. UVA is only an issue for sunscreens because of their well justified preferential protection from UVB (and UVA-II). The SPF is a proven indicator of quantitative protection with an erythema endpoint of unequivocal significance for a sunscreen’s primary function. UVA continues to be the focus of an intense international research interest. Increasing evidence shows that UVA provides benefits as well as causing damage, and it is clear that dose dependence is not linear but bell-shaped with regard to this relationship between benefit and risk. 

8. UVA does not exist on its own in Nature. But represents less than 5% of the total sunlight spectrum with which it is continuous.  Interpretation of experiments using UVA alone, and the conclusions drawn,  rarely takes this into account.  At the 2002 American Society of Photobiology conference in Quebec, David Mitchell from Texas University, Austin, presented work showing that a variant of the same fish model used by Dick Setlow, but without the high spontaneous incidence  of melanoma, was only susceptible to UVB induction of this most malignant form of cancer. In addition, at the 2002 MEPSA conference in Hobart, Ed DeFabo, and Frances Noonan presented a new mouse model for melanoma for which only UVB was effective. 

The UVA Ratio provides information and meaning consistent with that which we know about UVA, and perhaps more importantly it does not exclude anything we might in the future discover. 

9. If a UVA protection factor (PF) is sought then not only will a contentious endpoint be necessary but the PF derived must either follow the SPF with regard to any comparative product ranking in which case it is redundant, or be in conflict with it, in which case it will be confusing.

The UVA Ratio approach addresses a separate but complementary aspect of sunscreen protection.

With two categories of broad spectrum protection: Broad Spectrum and Extra Broad Spectrum, the message can be both meaningful and clear.

10. With a standard protocol and the  availability of adequate instruments and substrate (which does not leak like Transpore tape)  the UVA Ratio is easily and reproducibly measured.  No-one to my knowledge has suggested that the protocol for SPF evaluation should be compromised to accommodate  less than adequate instruments, so I will not here engage with suggestions that the measurement of the UVA Ratio should be compromised on such a basis.

We are revisiting the Broad Spectrum aspect of the Australian Standard with a view to delivering greater meaning and communicability.

11. International harmonisation is of concern to the global sunscreen industry for obvious reasons.

However the will to harmonisation would only be demonstrated by proposals tabled for international debate prior to their adoption.  This will is not demonstrated when it is argued that everyone should harmonise with the EU, or with the USA. This is globalisation, not harmonisation.

Sunscreen products are marketed to consumers on the basis of their real health benefit, and command a premium only on this basis.  The Australasian College of Dermatologists, the Australian Cancer Society, the Skin and Cancer Foundation of Australia, the Australian Society of Cosmetic Chemists and the Australian Consumer Society, together with considerable input over a long period of time with independent scientific researchers and clinicians tabled a proposal for the testing and performance parameters for the Broad Spectrum capability of sunscreens.  This proposal was aggressively opposed by members of the Committee who did not engage with this proposal in any way but to point to a different one drafted by a powerful European industry body also represented in Australia, but representing neither Australian consumers, their health, or Australian industry.

This same European industry body, COLIPA, and its Australian representative ACCORD, have already pushed through legislation regarding moisturisers with SPF (“Secondary” sunscreens) which does not bear scrutiny with respect to the health benefit conferred.  Due to the recommended use “sparingly” of moisturisers, the likelihood of a moisturiser delivering on the labelled SPF is scandalously low. Indeed it is difficult not to construe such labelling as an invitation to burn when it is well established that the majority of consumers use less than half of the amount of a Primary sunscreen product than we use for determining their SPF. 

The most recent iteration of the COLIPA method for evaluating UVA protection insists on a UV exposure step prior to measurement which is consistent with their use and in vivo SPF determination.  Such a step is easily accomplished and meaningful with regard to product photostability for the UVA Ratio, however if an in vivo SPF is used as in the calculation of a “UVA Balance” or UVA protection factor (and as proposed by COLIPA),  then the in vivo SPF value already takes into account any photoinstability and an in vitro pre-irradiation step will double up on this.

The UVA Ratio approach can be strongly argued on the international stage if the organizations represented on the Standards Committee have a combined will to do it.  This will essentially is a will to good science serving a health issue.   

Australia, as it maintains the dubious title of skin cancer capital of the world might not only take a leadership role on this issue, but justifiably resist compromises of that which it believes is in its best health interest.
___________________________ 

Closing words:

Complaints about sunscreen efficacy continue to be based on an unreasonable expectation that they should prevent sunburn like umbrellas protect from rain. A more apt analogy is that they protect like car seat-belts where their type, use and the force of impact are critical to the protection conferred.

The UVA ratio approach represents a best next step consistent with the need for an improvement of the meaning of Broad Spectrum capability of sunscreens, and the current state of knowledge.

__________________________
 

 References:

1.Paul, B.S., Parrish, J.A., The Interaction of UVA and UVB in the Production of Threshold Erythema. JID. 78:371-374 (1982)

2. Grange, R.W., Blackett, A.D., Ezra, A.. Matzinger, B.A., Sutherland, B.M., Kochevar, I.E., Comparative Protection Efficiency of UVA- and UVB-Induced Tans Against Erythema and Formation of Endonuclease-Sensitive Sties in DNA by UVB in Human Skin. JID. 85:362-364 (1985)

3. Bech-Thomsen N, Wulf HC, Poulsen T, Lundreg K: Pretreatment with long waver ultraviolet light inhibits ultraviolet-induced skin tumor  development in hairless mice. Arch. Drmatol 1988; 124:1215-1218

4. Elke Roser-Maass, MD; Erhard Holzle, MD; Gerd Plewig MD: Protection Against UV-B by UV-A-Induced Tan. Arch Dermatol: Vol 118,(1992) 483-486.

5. Nghiem, D. X., Kazimi, G. Clydesdale, H. Annanthaswamy, M. I., Kripke and S. E. Ullrich (2001) Ultraviolet A radiation suppress an established immune response; implications for sunscreen design. J. Invest. Dermatol. 117, 1193-1199.

6. Skov, L., Villadsen, B. J. Ersboll. J. C. Simon, J. Barker and Baadgaard O. (2000) Long-wave UVA offers partial protection against UVB-induced immune suppression in human skin. APMIS 108, 825-830.