Sun protection has come a long way in the last 20 years. Julia Wray and John Woodruff report from the tenth biennial Sun Protection Conference held from 3-4 June, Royal College of Physicians, London
The worldwide sun protection market is worth $4.5bn, according to analyst Euromonitor International, and ingredients offering sun protection are being incorporated into an increasing variety of skin care products. So it came as little surprise that the tenth International Sun Protection Conference attracted delegates from as far afield as the US and Australia.
Keynote speaker Ronnie Marks (Cutest Systems) began the first session with The clinical sequelae of solar elastosis. Defining solar elastosis as the altered subepidermal dermal connective tissue due to continued solar exposure, Marks used images of histological sections to demonstrate the altered staining properties and morphology of sun damaged dermal connective tissue, which showed the breakdown of the fibrous dermis into “spaghetti and meatball” fibres. Marks believes collagen loss, and its substitution by this degenerate elastotic substance, to be responsible for most clinical sequelae in photodamaged skin.
Delegates were then shown examples of skin disorders potentially caused or influenced by solar elastosis including wrinkling; cutis rhomboidalis nuchae, or sailor’s skin; telangiectasia, caused by the dilation of individual large venules; senile purpura; senile comedones, or blackheads; citrine skin; and triradiate/stellate scars, the lesions most often found on the extensor surface of sun damaged forearms.
Veronique Bataille (King’s College London & West Herts NHS Trust) followed with Genetics of photoageing and skin cancer susceptibility. She ran through the physical signs and histological processes of photoageing before focusing on the genetic factors involved. Particular attention was paid to a study of 4,000 twins, which took skin phenotypes, skin and eye colour, skin type, solar elastosis and solar keratosis into account, and which featured a lifestyle and medical history questionnaire. The twin model, said Bataille, showed both dermal thickness and naevi (moles) to be 60% heritable, pointing to a strong genetic factor in determining how people age.
Bataille drew attention to the recent discovery of two naevus genes, also found replicated in large melanoma samples. But she pointed out that the twin study showed subjects with excess naevi age less than those with few, and telomere length – telomeres being non-coding strands of DNA at the end of each chromosome that reduce as you age – to be strongly related to naevus count, with less moley people having shorter telomeres, associated with frailty.
EFFECTS OF EXPOSURE
The effect of near infrared (NIR) light on the production of free radicals (ROS) in skin was the theme of Louis Ferrero’s (Coty Lancaster) presentation. Ferrero detailed a study carried out by Zastrow et al using different infrared irradiances on ex vivo skin samples and measuring levels of the most reactive ROS (hydroxyl radicals, superoxide radicals and lipid radicals) using a spin trap PBN (phenyl-tert-butylnitrone).
The ex vivo experiments were said to show for the first time that NIR light produces free radicals in human skin tissue, with values at 40°C for an irradiation time of 1,600 seconds (0.8. 1012 rad/mg), around one quarter of the amount of free radicals created by a UVA/UVB dose at the point of erythema (3.5. 1012 rad/mg).
Ferrero added that in addition to the dose the NIR light initiated, skin temperature (taken at a depth of 1mm below the skin surface) was found to influence free radical production and because long and intense infrared exposure boosts skin temperature, higher free radical production values could be expected. Consequently he suggested that antioxidants or free radical scavengers be advised for long periods of sun exposure under conditions where the internal skin temperature reaches high values.
While it is possible to quantify some effects of sun exposure on the skin in vivo, it is more difficult to gauge others. Marisa Meloni (VitroScreen) discussed the benefits of in vitro techniques as an answer to UVA research needs in Molecular modifications of dermal and epidermal biomarkers after different UVA exposures on reconstructed human full thickness skin. Meloni detailed work investigating the biological relevance of full thickness (FT) skin models in the response to UVA exposure by monitoring extra-cellular matrix (ECM) and epidermal biomarkers.
She explained that the cellular response to UVA radiation at a molecular level was mediated by specific gene signatures and gave details of a study in which FT skin models were given single UVA doses of 2, 6 and 12 J/cm2 and readings were taken at two hours, six hours, 24 hours and seven days after exposure; a repeated dose of 6 J/cm2 split into 2 J/cm2 over three days was also delivered. Epidermal markers (TNF-α, IL-1α, IL-10, IL-17, involucrine, glutathione peroxidase and glutathione reductase) were monitored, as were those in the DEJ (integrine β-1 and collagen VII) and the dermis (fibrillin, decorin, elastin, collagen I, MMP-9 and MMP-1). The results for elastin, said Meloni, were particularly significant, with repeated exposure eliciting a downregulation at two hours indicating damage of the elastin gene expression. Also singled out were the results for collagen I, in which a downregulation at 24 hours (irrespective of dose) signified damage followed by recovery. Meloni added that molecular markers could be used to quantify the type and mechanism of UVA protection offered by topically applied products.
Next up was Steven Wang (Memorial Sloan-Kettering Cancer Centre) on the challenges of educating US consumers about sun care. He acknowledged the success of public health programmes in raising awareness but also noted that people often used sunscreen as their only defence against sun exposure, a strategy at odds with health messages advocating sun avoidance and protective clothing as well. A survey of 415 individuals in New Jersey found that only 33% knew that sunscreen should be applied 30 minutes before going outside and just 32% knew to re-apply every two hours. In addition, 51% believed that a higher SPF meant better protection against UVA. Only 19% answered correctly that there was not enough information available to determine whether this was the case.
Wang suggested that any public awareness campaign should have an instructional message and a motivational one, tailored to different demographic groups.
The second keynote presentation, Sun protection, skin colour and vitamin D, came from Jean-Paul Ortonne (University of Nice-Sophia Antipolis). He explained the cell signalling pathway of UV induced tanning focusing on the POMC gene stimulating role of p53 in keratinocytes and the action of the resulting α-MSH on melanocytes, whereby tyrosinase activity is stimulated via the cAMP pathway leading to melanogenesis. He then identified the principal genes determining human skin colour as melanocortin receptor 1, agouti signalling protein, pink-eyed, membrane associated transporter protein and cation exchanger.
Ortonne suggested that humanity’s ancestors were probably pale skinned (the African apes from which they descended having had light skin protected by bodily hair) but had evolved more melanin to help protect against sunburn, skin cancer and folates photodegradation. The humans that moved out of Africa into regions with lower sun exposure, said Ortonne, had less need for protection and greater difficulty synthesizing vitamin D, meaning that their levels of melanin production eventually reduced. An overview of the current debate over the safe level of sun exposure for the production of vitamin D rounded off the talk.
IN VITRO METHODOLOGIES
One of the industry’s current goals is to find in vitro sunscreen measurement methods to replace invasive tests on human volunteers. Joe Stanfield (Suncare Research Laboratories) addressed this in Optimising agreement between in-vitro and in vivo measurements of sun protection.
First, the limitations of existing in vitro measurement methods as a way of determining the UVAPF of non-photostable sunscreens were explored. Stanfield then recommended a more convenient alternative, the Integrated Absorbance Spectrum, which enables scientists to measure the in vitro UVA and UVB absorbance, determine the uniformity of the absorbance spectrum and calculate SPF factor using an algorithm that models the behaviour of a photolabile sunscreen during continuous UV exposure.
Stanfield outlined the procedure as follows: measure the absorbance spectrum before and after radiation with a UV dose in MEDs (1 MED being equal to 20 mJ/cm2) of 25%, 50%, 75% and 100% of the expected SPF. Calculate the applied and transmitted effective UV doses in MEDs and plot a graph that enables the calculation of SPF. Once the absorbance values have been adjusted using a constant correction factor to agree with the in vivo SPF, determine the time point at which the sunscreen transmits an effective UV dose of 1 MED (tMED) by interpolation from elapsed times for UV doses. From this, said Stanfield, it is possible to compute transmitted and applied UV doses for each wavelength at tMED and to then find both the transmission (the transmitted dose divided by the applied dose) and the integrated absorbance for each wavelength.
John Stanton (Dermatest) explained the process used to increase harmonisation and reproducibility in Validating for in vitro UVA testing. He focused on an International Organization for Standardization (ISO) Ring Study to determine the influence of irradiance on test outcomes, which involved nine countries and featured tests on five sunscreens to identify the key parameters for validation. Instruments were tested for accuracy, transmittance and linearity while moulded PMMA was felt to be the best available substrate. To reduce error further a new standardised application system was specified. The study also concluded that the test temperature should be no more than 40°C, that other pre-irradiation factors like the influence of flux ought to be taken into account and that results should be interpreted with an ISO standard spreadsheet for data entry to minimise the potential for calculation or transcription error.
Stanton mentioned that a second ISO Ring Study was currently being conducted to address further issues such as control of pre-irradiation, higher sample dose and rougher plates.
Reproducibility is crucial when conducting in vitro tests to determine a sunscreen’s SPF and the substrate’s surface microtopography is key to achieving this. Marc Pissavini (Coty Lancaster) discussed reproducibility in his presentation, Importance of the substrate surface microtopography. Pissavini recommended PMMA plates as the most effective substrate, but noted that the roughness of the plate (PMMA ones come in two roughness values) affected the in vitro SPF in that “when you increase roughness you decrease SPF”. PMMA plates are traditionally made from sandblasted sheets that are then cut to size. But it is difficult to ensure that a plate from the centre has the same roughness as a plate from the corner and roughness has been known to vary by 50%. As an alternative, Pissavini suggested injection moulded PMMA plates said to vary significantly less (5%) enabling maximum reproducibility.
Mike Brown (The Boots Company) followed with Adaptation of the Star Rating Methodology to take account of photo-degradation in line with EC Guidelines, which addressed the EC’s 2006 recommendation. While agreeing with the EC’s statements that current in vitro measurements were too brief to challenge potential photodegradation and that the sunscreen must be exposed to a dose of UV light to simulate the degradation that might occur during normal outdoor exposure, Brown criticised the recommended PPD method for UVA for involving unrealistic UV spectrum, intensities and doses. Brown explained that the irradiance of the solar simulator used in the PPD test (up to 1,300W/m2) dwarfed that of actual sunlight (71W/m2 at 20° South). He also drew attention to the total dose of UV exposure used in the PPD test (300J/cm2) compared with the 19J/cm2 that skin would be exposed to during one hour of peak summer sunlight at 40° North.
Brown contrasted this with the Star Rating Methodology, explaining how the parameters for a “realistic” alternative to the PPD test – including the irradiance range between 45W/cm2 and 90W/cm2, final fixed dose of 17.5J/cm2 and temperature between 20°C and 40°C – were arrived at.
Also focusing on UVA protection was Dominique Moyal (L’Oréal). Her presentation, emphasising the need for standardisation and harmonisation of measurement methods, drew the first day of the conference to a close. She explained that existing methods – PPD, PPD in vitro, the different in vitro methods used by Boots and the FDA etc – used different plates, different roughness, different amounts of product, different UV doses and different criteria and labelling. With this in mind, Moyal posed the question: “How much are the results influenced by the measurement conditions?” She then showed delegates one test, part of a study comparing Boots conditions with Colipa (PPD in vitro) conditions, in which the UVAPF varied by 11.5 points. The results of this study – plus three others comparing similar methods – showed not only that different methods often yield different star ratings for the same sunscreen but also that a three star rated sunscreen may not necessarily have the 1/3 UVAPF/SPF ratio suggested by the EU Commission. Increased harmonisation was necessary, she concluded.
MEDIA & MARKETS
Day two of the conference opened with Emma Meredith (CTPA) asking Can we really achieve protection from media scare stories? Cosmetics, including sun protection products, frequently suffer from bad and mostly ill informed media attention. Meredith showed typical examples claiming that sunscreens did not offer the protection claimed; that they do more harm than good; that they cause skin cancer; that they cause endocrine disruption; that they are responsible for a lack of vitamin D in people and that they kill corals. Nanotechnology also attracts bad press and this particularly applies to inorganic sunscreen materials.
The CTPA tries to combat these harmful messages by engaging with the media and the public and has formed links with other associations and through its own website [www.thefactsabout.co.uk] and theirs it endeavours to contradict some of the more outrageous negative claims. On the subject of sun products the CTPA message is that like all cosmetics, sunscreens are subject to strict European laws which ensure that sun protection products are safe to use and that any claim made, such as an SPF number or UVA protection, must be substantiated before the product is put on the shelves.
Sunscreen regulations in international markets was the title of Debra Redbourn’s (dR Cosmetic Regulations) presentation which sought to guide delegates through the minefield of which UV absorbers can and cannot be used around the world. During the last two years there have been six absorbers put under review in the EU, which has led to PABA being banned; camphor benzalkonium methosulfate having its maximum concentration reduced from 6% to 3%; and benzophenone-3 being reduced from 10% to 6%. Meanwhile 4-methyl benzilidene camphor is allowed at up to 4% and the use of micronised zinc oxide is still banned and awaiting further review.
The EU, ASEAN member countries and South Africa consider sun protection products cosmetics but in the US and Canada they are licensed drugs and Redbourn explained the procedures for submitting products for licence and how to label products that are accepted. Returning to the EU, she explained the current Commission Recommendation published in 2006 on sunscreen products and the claims that are allowed, and disallowed. While a recommendation is not a legal requirement, manufacturers are expected to comply and an estimated 95% of products now do so.
Frank Nash (P&G) discussed Current opinions on the human safety of titanium dioxide and zinc oxide. The large surface area per unit mass of nanoparticles makes them highly reactive, which has raised concerns in the media over toxicity to humans and damage to the environment.
Nash presented a summary of the extensive work undertaken by recognised authorities to investigate the toxicity of nanoparticles of titanium dioxide and zinc oxide. The adequacy of test methods was investigated and the conclusion was that current toxicological testing was satisfactory for nanomaterials as such tests were already deemed adequate for particles of greater or lesser size. Dermal penetration studies failed to find either zinc oxide or titanium dioxide particles that penetrated beyond the top three layers of the stratum corneum and no instances of genotoxicity or phototoxicity were found. Nash said that a database covering guideline hazard-based toxicology studies has been developed for nano titanium dioxide and zinc oxide and that results support low level of toxicity equivalent to pigment grades of these metal oxides. Skin penetration studies did not indicate absorption of nanoparticles by the skin and results show that toxicity is mainly correlated with chemistry and not particle size.
PHOTODAMAGE & PROTECTION
Nowhere is the understanding of the need for sun protection more important than in Australia where 50% of the population will be treated for skin cancer in their lifetime. John Stanton illustrated the problems of the high levels of UV radiation that reach Australia and its population and expanded on various sun awareness programmes. The country has launched a new ISO standard for sun products that takes into account water-resistance and UVA protection and introduces a new category of Extra Broad Spectrum for products with an SPF>50.
It is now accepted that UV radiation from the sun causes skin damage and William Johncock (Symrise) presented New findings in the causes and prevention of photodamage of human skin. Recent research has identified another very important mechanism in UVB induced cell damage, said Johncock, which according to some dermatological experts accounts for at least 50% of the damage, including skin cancer and premature ageing. He discussed the biochemistry of cell damage caused by a toxic response in the skin by UV activation of the aryl hydrocarbon receptor (AhR).
The AhR is a protein complex found in the cytoplasm of every cell and its primary function is thought to be the metabolism of chemical species. It typically binds to flat aromatic hydrocarbons and in many cases makes them toxic via transportation from the cytoplasm into the nucleus where they interact with DNA. Transport of foreign chemical toxins by AhR activation results in oxidative stress, skin irritation, atopic dermatitis, skin ageing via MMP-1 induction and skin cancer via induction of cytochrome P450 enzymes. Johncock proposed the use of AhR antagonists to inhibit this mechanism and provide enhanced protection against photoageing when used in combination with UVB filters. It should also reduce UVB induced inflammation and immunosuppression and protect against photocarcinogenesis. Johncock proposed the use of a material codenamed Bio 1031 as the antagonist of choice.
An important section of the conference was sunscreen formulation and there were three presentations on this subject. Christine Mendrok-Edinger (DSM) looked at Maximising efficiency of high SPF products while maintaining an optimal skin feel. The paper covered choice of UVB filters and synergistic combinations, sensory performance and quality of the sunscreen film. It also discussed UV filter compatibilities and UVA filter selection was looked at with the aim of optimising spectral coverage while maximising photostability.
Much work has been done by DSM to find the best UV filter combinations and efficiency ratings are awarded by dividing the SPF attained by the % of filter necessary to obtain it. Mendrok-Edinger said the concept of combining UV filters with very different physical properties proved to be very powerful with best results provided by a combination of a silicone-based filter (P-15), a water-soluble filter (PBSA) and two oil-soluble filters (BMDBM, OC) giving SPF 45 with 14.6% UV filter. Stabilisation of filters and choice of emulsifier were also discussed.
Helene Hine (Croda) took the title Sunscreen formulation in the changing regulatory environment. EU Commission guidelines suggest that sunscreen products should be sufficiently effective against UVB and UVA radiation and that the UVA protection factor must be at least 1/3 of the claimed SPF at a critical wavelength of not less than 370nm. Formulations based solely on inorganic sunscreens can meet EU, Japanese and Australian requirements, but fail to achieve the highest ratings on the Boots system or the proposed FDA system. One method of meeting this target is to combine transparent TiO2 with manganese-modified TiO2. Another way is to combine ZnO with TiO2; a ratio of 6:4 ZnO:TiO2 will give a minimum 0.33 UVAPF:SPF.
A third formulation presentation from Uli Osterwalder (Ciba-BASF) described The long way towards the ideal sunscreen. He said that it should protect against UVB and UVA and reduce the quantity of the UV radiation without changing the quality of the UV radiation that reaches the skin. He said to achieve the ideal we need to consider the technology and means of measurement and assessment and the standards and compliance with them. He believes the technology has come a long way but pointed to patent and regulatory issues that are hindering progress.
Measurement and assessment still has a long way to go, with problems surrounding human volunteers but no in vitro alternative for measuring SPF. Standards are being set by individual countries and more needs to be done to obtain global harmonisation and compliance with the standards.
The title of this year’s biennial sun protection conference was Towards the perfection of protection and this was the title chosen by chairman of the second day Brian Diffey (Newcastle University) for his presentation. Diffey reported that in surveys the measure regarded as being the most important was the use of sunscreen. He then asked whether given that sunscreen use is generally regarded as the ‘ideal’ sun protection measure and there is little question that the technical performance of sunscreens have improved dramatically over the past 20 years, is perception borne out by reality and have we now succeeded with the perfection of protection?
In theory an SPF of 10 or more should be adequate to prevent sunburn in southern Europe and an SPF of 15 should be suitable for tropical sun exposure. However, such products often prove inadequate because of poor application by the user or loss through perspiration, bathing or abrasion. Diffey believes that because of these factors most people only get one third of the protection level expected. His argument was that people use the quantity they feel comfortable with and in this sense are using the correct amount; it is the labelled SPFs that are misleading.
Diffey concluded that while the formulation of sunscreens has undoubtedly improved, the notion that sunscreens provide unequivocal protection against the deleterious effects of sun exposure remains elusive. Furthermore sunscreen use during recreational exposure in periods of high insolation appears to be a behaviour pattern followed by the minority. Future efforts should focus on compliance so that most people want to apply sunscreen during high dose-rate sun exposure and benefit from the reduced risk of harm which improvements in technology promise to deliver.