7-2013

English EditionInternational Journal for Applied Science

• Personal Care • Detergents • Specialties

J. Vollhardt, A. Janssen, Ch. Saecker

Modern Sunscreens that Protect from more than just Sunburn

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J. Vollhardt, A. Janssen, Ch. Saecker*

Modern Sunscreens that Protect from more than just Sunburn

■ Sunburn and what happens atlower UV dosages?

If our skin receives UV light with the firstray damaging effects will happen to vari-ous cellular and extracellular constituents.For keratinocytes, after »enough« cellshave been »disabled« by a certain UV-in-

duced damage level and undergo theprogrammed cellular death, a distinctbuildup of inflammatory cytokines oc-curs. The thus initiated inflammationprocess causes blood vessels to widen,and this turns the skin red. A sunburn be-comes manifest macroscopically not on-ly in skin reddening but also in a grow-

ing level of pain on the affected spot. Thecorresponding energy dosage necessary toinduce this skin answer is called one min-imal erythemal dosage (1 MED). Dosagesbelow this value usually do not induceany visible skin redness, with the excep-tion they are received subsequently fora longer period of days. If a single UV

Introduction

After 3 decades of intensepublic campaigns sun pro-tection is in the mind of al-

most every consumer in particularif it concerns holiday or sport ac-tivities. Does this mean that in-dustry stakeholders and con-sumers can lean back? Surely not.There is still a lot more work andeducation on safe sun exposure todo, in particular because only onecountry so far, Australia (1), hasachieved a beginning decline ofthe melanoma incidence. Holidaysand sport themes are often com-municated together with sun pro-tection messages – with a com-pelling reason: a significant por-tion of the annual UV exposuredose is collected in these

episodes. But to draw the wholepicture: more than half of the UVdosage is not linked to vacationtimes but rather to day by day ac-tivities such as gardening, grillparties or lunch breaks. Peoplehave significantly lower aware-ness for sun protection in thosesituations which might result inoccasional localized sunburn, e.g.the facial area. In holidayepisodes most consumers havelearnt how to avoid sunburn oflarger skin areas; however, quitefrequently they still have localizedweak sunburns on super-exposedskin parts or areas which hadbeen treated only sparsely withsunscreen. Sunburn does causepain and significant discomfort

and therefore represents a strongdriver to apply sun protectionproducts. Most people considerthe avoidance of sunburn as a suc-cess signal for their personal pro-tection strategy and feel on thesave side if they succeeded in do-ing so. But is this really true? Aredosages below the erythemaldose level (1 MED) well compen-sated in our body? This articlelooks at such dosages in a few di-mensions, e.g. DNA damage asmutagenic marker, oxidativestress as anti-aging initiator andimmunosuppression as a cancerenhancement marker. It also givesrecommendations based on thefindings to protect people of UVradiation beyond sunburn.

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dosage does not cause sunburn it iscalled suberythemal. The energy or duration of UV radiationnecessary to induce sunburn is not con-stant and can vary a lot from person toperson mainly depending on skin type.Sunburn is also wavelength dependentas UVB is more damaging than UVA. Be-ing in a holiday location in the tropicsmakes our skin burn faster, not only be-cause of a general higher radiation in-tensity but also because at that latitudesunlight contains more UVB than e.g. inEurope (Table 1). But it is important tokeep in mind that sunburn is not 100%UVB based. There is also an energy levelor time point at which pure UVA radia-tion would cause erythema as well if UVBwere filtered out (Table 2). This situationmay evolve with sunscreens providing noor little UVA protection. When reporting on human trials involv-ing UV radiation, the wavelength and in-dividual sensitivity dependency of theMED is less suitable and may lead to con-fusion in data comparisons. Additionalparameters would have to be measuredand reported to make experiments com-parable. The Standard Erythemal Dosage(SED) has therefore been introduced (2)to avoid or define dependencies. For areference example: 1 MED for a skin type2 person is about 2 SED. Table 2 (3-6) listsaverage energy values to induce 1 MED ina skin type 2 person of some commonlyused light sources, note the much highernumber for UVA to induce sunburn.

■ Molecular components relatedto sunburn and evolvement of UV damage until sunburn

It is widely accepted that sunburn islinked with DNA damage in the cellularnucleus, followed by apoptosis of thekeratinocytes and in consequence in-duction of an inflammation, which leadsfinally to skin redness. However not allconnections in this cascade of events arefully understood. The most prominentprimary target for UV interaction withskin is DNA. UVB light gets physically ab-sorbed e.g. by the thymine chromophore.The epidermis is densely packed withcells and therefore UVB does not pene-trate much deeper than the basal layer

due to absorption and some back scat-tering. The absorbed energy allows thebase pairs of the DNA to undergo a va-riety of reactions which lead to alter-ations in the structure of DNA. The ge-netic code at that structurally altered lo-cation is not correctly readable anymoreand thus could give rise to mutations.Two neighboring thymines in the DNAstrand are prone to a particular muta-tion: they form in a photo-catalyzed re-action a dimer, called cyclobutane pyri-midine dimer (CPD) or more specific,thymine dimer (TT). Fortunately, our cellshave evolved several DNA repair mecha-nisms such as the nucleotide excision re-pair (NER). While it is well known thatUVB is the major source of DNA damage,only recently it has been shown that UVAcould also induce direct DNA damageparticularly in deeper layers of the skin(7). UVA light interacts also with DNA inmore indirect mechanism through for-mation of excited oxygen species whichfinally might lead to the formation ofCPDs, 8-oxoguanine and strand breaks. p53, a key protein, orchestrates the re-pair process. It also initiates apoptosis,the programmed cell death to protectagainst mutagenesis. Such affected cellsare called sunburn cells (SBCs). Damageon p53 itself and persisting mutations ofthat protein are very critical as they can

represent one major route to carcino-genesis. The complex repair process, par-ticularly for the CPDs, takes place with-in hours and days and is therefore gen-erally much slower than the time to pro-duce the damage under solar radiation.Different molecular biological markersare known to track the buildup of thisdamage and repair process, which hap-pens unnoticed by the consumer untilthe skin shows visible signs of rednessdue to exposure to erythemal UV dosages(> 1 MED). Indicative damage markersafter UV radiation can be: relative num-ber of SBCs and CPDs. Also monitoringof p53 by immunofluorescence can behelpful, as it indicates the cells’ begin ofrepair. In addition to molecular biologi-cal methods requiring biopsies, measure-ment of the erythemal index representsa sensitive technology to follow up thesubsequent rise towards sunburn beforeit is really visible to the human eye.

■ Damages revealed before onset of sunburn after single and subse-quent suberythemal UV Exposure

Fig. 1 shows the slow evolvement of skinredness by a series of subsequent subery-themal dosages (11 x 0.6 MED of SSR)

UVB : UVA

Natural day light, Europe noon, noon time, June 1 : 25

Natural day light, tropics noon 1 : 18

Solar Simulated Radiation (SSR, artificial light for SPF measurements) 1 : 10

Table 1 Light sources: Proportional energy ratios between UVB and UVA light

Type of Light Energy necessary to induce1 MED in a skin type II

Monochromatic UVB (300 nm) median 25 mJ/cm2

Monochromatic UVA (360 nm) median 32 J/cm2

Simulated Day Light (SDL) 15.2 J/cm2

Sun (295–400 nm) ~5–12 J/cm2

Solar Simulated Radiation (SSR) as used for SPF measurement ~2 J/cm2

Table 2 Energy values of certain light sources to induce 1 MED in a skin type 2 person

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volunteers of skin type I and II were ex-posed to (8). At a value of about 80 skinredness gets visually perceivable. Overthe whole period of 11 days there seemsto be a gradually rising level of damageindicated by progressing skin redness(blue line, Fig. 1). During the first 8 – 10days this damage goes on unnoticed, on-ly at the last day it seemed to have be-come finally manifest in sunburn ap-pearance. A low level sunscreen (SPF of7.5) was enough to suppress a majorevolvement of skin redness, but - is thisreally an indication for the complete ab-sence of DNA damage? We therefore in-vestigated the CPD level with biopsies(Fig. 2).Fig. 1 also suggests that there seems tobe not much damage for a single radia-tion period, e.g. at day 1. This aspect hasbeen addressed by several authors (5,8-10), who analyzed biopsies of skin typeI, II or III volunteers after a single radia-tion of 0.5 MED with several lightsources, including also pure UVA light(11). CPDs could already be detected inkeratinocytes and melanocytes, as an in-dicator of DNA damage. Also p53 seemsto be up-regulated, indicating the switchon of the repair signal in skin type II andIII.We therefore investigated the CPD levelwith biopsies. Fig. 2 shows significantlyelevated DNA damage levels after 5, 11and 12 days of suberythemal radiationfor the untreated area. This means theerythema index does not parallel thepresence of CPDs. The DNA repair is al-ready leading to a balance of newly in-coming and already repaired damage.After the last radiation (day 12) the CPDvalue is going down, which is indicatingsuccessful repair. A broadspectrum sun-screen having only an SPF of 7.5 is ableto cause a significant protection againstDNA damage. However, the low protec-tion level was not fully sufficient to sup-press CPD formation completely com-pared to the non-radiated site, so a stillsmall level of DNA damage persists. Similar observations had also been madein a study with 9 times subsequentsuberythemal UV radiations at 0.25, 0.5and 0.75 MED (12), in which also the dif-ference of SSR used for SPF testing anda simulated day light (SDL) had beencompared. A radiation of only 0.25 MED

of either SSR or SDL was enough to gen-erate p53 upregulated cells. SBCs werepresent at a significant level already atonly 0.25 MED SSR, while SDL needed 0.5MED to generate a similar number.

■ UVA radiation is setting an agingprocess into motion

Visible signs of skin aging become evi-dent as wrinkles, in particular around theso called »crow feet« area, but also an

uneven skin tone (13) delivers informa-tion for a visional judgment on age. Thedesire to look attractive is high, being themain driver of the global demand foreffective treatment concepts. A secondstrategy, which actually should be theprimary one to fight signs of aging is toprotect skin against their origin beforeaging signs appear or get worse. In par-ticular UVA induces a multitude of ef-fects which lead to visual skin aging phe-nomena. Most often UVA-induced changesstart by UVA light generating oxidative

Fig. 1 Erythema index during 11 subsequent suberythemal dosages of 0.6 MED. Thesunscreen used was broadspectrum and had an SPF of 7.5

Fig. 2 Evolvement of CPDs with 11 subsequent suberythemal treatments with 0.6MED. Pictures represent day 12, a (unprotected), b (sunscreen SPF 7.5)

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stress in the tissue. An action spectrumhas been measured for this. Multipliedwith the solar radiation spectrum the re-sulting solar radical generation spectrumshows the strongest peak around 360 nm(14), which indicates that most oxidativestress caused by UV originates from UVA.Unfortunately UVA penetrates deep intothe dermis and can there initiate partlyirreversible damage of cell constituentsand matrix proteins. Over the years mod-ified proteins could build up as they arehard to metabolize and form e.g. the ba-sis solar elastosis. The inhomogeneity ofprotein distribution causes also an un-even whiteness distribution of the skin.Considering that UVA is present muchlonger during the day time than UVB,sunscreens should therefore be allequipped with a sufficiently strong UVAprotection. Day care formulas may evengo over the recommended minimumguidelines to achieve an extra benefit infighting the face changing effects ofUVA.

■ Suberythemal UV radiation leadsto immunosuppression

Our skin has several lines of defenseagainst deleterious UV effects. The skin’simmune system can be seen as a lastfortress in the fight against cancer for-

mation. It detects mutated cells and de-stroys them. However, the immune sys-tem reacts very sensitive to UV stress. Re-cently an action spectrum for immuno-suppression has been established (15). Itshows two peaks, a smaller one at 300 nmand a huge one in the UVA region peak-ing at 370 nm. It has been shown thatonly 0.3 MED is enough to damage theimmune response of the skin towards

allergens (and in essence also towardsmutated cells). The Mantoux reactionagainst tuberculin has been utilized tomeasure this effect (16) (Fig. 3, bluebars). We were also able to see disap-pearance of Langerhans cells upon sub-sequent radiation of 0.6 MED (8) (Fig. 4,blue bars). Seité (4) had observed an sig-nificant immunosuppressive effect al-ready at 0.25 MED. A SPF 7.5 broadbandsunscreen protected the Langerhans cellssignificantly against the suberythemalUV radiation (Fig. 4, pink bars). Interest-ingly, it was found that topical Niaci-namide, also known as Vitamin B3, al-most completely preserved the immunestatus of the volunteers exposed to 0.3to 1 MED SSR (Fig. 3, pink bars).

■ Two typical UV exposure scenar-ios – is there a need for more pro-tection?

1st Scenario – Shorter periods ofexposure in summerMany leisure activities including lunchbreaks happen around and at the zenithof sun, where the UVB intensity is thehighest. During lunch people are oftenfacing the same angle towards the sun,so that there is little relief by changingexposure to other body areas. Some parts,

Fig. 3 Immunosuppressive effect of erythemal and suberythemal SSR. Protection canbe achieved with Niacinamide (15)

Fig. 4 Influence of 11 subsequent suberythemal radiations with 0.6 MED on the num-ber of Langerhans cells

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e.g. the nose tip or ears can actually behit perpendicular by the sun, whichmeans reception of the full UV dosagecompared if the sun had a certain angleto the plain of the skin. The risk of get-ting sunburn varies of course with theskin type. Skin type I and II, both partic-ularly sensitive, would have most likelyno longer than 0.5 h under those condi-tions until they reach 1 MED and exhib-ited a slight sunburn. Skin Type III wouldhave eventually about 15 - 30 minuteslonger and Type IV would most likelyhave no burn symptoms during a lunchbreak.Easily sunburn can be avoided duringoutdoor lunch or other shorter outdooractivities by utilizing a SPF 15 UVB basedsunscreen, a formula type often realizedin former generations of day care formu-las. However, such a formulation principlewould leave the door open for UVA basedpremature aging effects. In addition therecould also be a UVA based sunburn. Insolar radiation the UVB contribution isonly 80-85 %. UVA light is clearly muchless effective in causing sunburns, but onthe other side it is 25 times more abun-dant. At the French Riviera e.g., if some-body were solely protected against UVBit would take about 2-3 h in noon timefor a UVA sunburn of a non-tanned per-son with skin type II (4). UVA is still verymuch present in morning and afternoonhours, when it is »UVB safe«. Even moreconcerning are the devastating prema-ture aging effects of UVA light. Thereforeday care formulas need to be equippedwith a functional UVA protection screen.On top of that should be also an im-muno-protective agent, e.g. Niacinamide,because already lower levels of radiationcould cause damage here as shown above.People typically apply significantly lessthan 2 mg/cm2, which call for addition-al measures for facial care products. Theresidual oxidative stress by still transmit-ted UVA light needs to be taken care of.Therefore a day care formula shouldalso contain an anti-oxidant complex.Combinations of Vitamins and plant ex-tracts offer good solutions here. A sig-nature plant associated with blue skyand high sunshine radiation is Edelweiss(Leontopodium nivale, subsp. alpinum).It grows only in high altitudes up to3000 m with a lot of UV radiation and

has developed powerful anti-oxidantdefense systems to survive in this habi-tat. The constituents are able to protecthuman skin too (17). It is a protected wildlife species; however, due to high alti-tude alpine cultivations according to BioSuisse organic standards this material(ALPAFLOR® EDELWEISS) is available tothe personal care industry. The design and realization of facial daycare formulas can be particularly chal-lenging to comprise all above-describedfunctionality and together with desir-able sensory features. Day creams shouldneither be too greasy or too glossy norshould the play time too long. After arather quick dry-out, there should be anice, silky and matt finish. Extra careclaim formulas could purposely leave aperceivable lipid film with a little thick-er residue. Usually most UV filters add anoily and greasy feature to the formula,and generate a lot of shine in the residueon the skin after the rub out. For broadUV spectrum functionality UVA and UVBfilters are a must but careful selection ofthe UV filters and building on the SPFcontributing synergy between the UV fil-ters will help to tweak the formulas to-wards a drier, less greasy direction. UVfilters occupying the water phase of

emulsions, like Phenylbenzimidazole Sul-fonic Acid (PARSOL® HS), show very goodperformance with no oily or greasy skinfeel. Polysilicone-15 (PARSOL® SLX) addsnot only synergistically UV protectionperformance to such a system, but alsoa silky skin feel. The high-spreading sili-cone feature of this UVB filter implies anauto-rearrange on the skin to correct lo-cal film irregularities and weak coveragespots. Formulas with Polysilicone-15(PARSOL® SLX) therefore perform usual-ly much better on human skin than on invitro plates. The high SPF boosting syn-ergy between Phenylbenzimidazole Sul-fonic Acid (PARSOL® HS) and Polysili-cone-15 (PARSOL® SLX) had been clear-ly demonstrated by in vivo SPF determi-nations (18).

2nd Scenario – Summer holidayexposureThis 2nd scenario includes beach holidayswith quite intense and consecutive UVexposure with a typical length of about1-3 weeks. A skin type II person couldtheoretically easily gather 10-15 MED ona clear day in Southern Europe in thesummer. But as even sun worshipper ona deck chair move and turn their bodies

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and the angle of the plain of the skin isoften not 90° towards the sun the actu-al daily UV dosage received is rather thehalf of the theoretical maximum. How-ever, certain skin areas, let us name themsuper-exposed areas, e.g. head, top ofthe ears or shoulders and the nose tipcould receive a significant higher UVdosage due to a preferred orientation. Itis strongly recommended to use addi-tional sun protection for these super-ex-posed skin parts. Very recently a sun ex-posure investigation concluded on Tener-ife (19). The participants wore wrist dosi-meters, and in only 6 days each of the 25subjects picked up 57 SED in total on av-erage, which is about 43% of the annu-al dosage of a Danish indoor worker. Thisquite intense and highly cumulated UVdose calls for good sun protections mea-sures. A SPF 15 product, as recommend-ed by authorities e.g. in UK or US wouldprotect against sunburn in those cir-cumstances if applied according to guide-line, with 2 mg/cm2 and with re-applica-tions. But there is more to consider thanonly sunburn. The fully correct usage ofsuch a SPF 15 sunscreen would still re-sult in 0.3-0.5 MED of suberythemal UVradiation on average and super-exposedsites would receive even a higher dosagewith all the consequences and risks de-scribed above. Products with much high-er SPF are therefore recommended forbeach holidays or other full-day outdooractivities. It is a well-known fact that people applya smaller amount of sunscreen than rec-ommended and required to achieve thelabeled SPF factor (20). The SPF that ma-terializes then for the consumer is there-fore often only a fraction of the labeledSPF (21, 22). Typical application amountsvary between 0.4 to 0.8 mg/cm2, whichis reducing the (labeled) SPF by about 5to 2.5 times. To nevertheless cope withthe significant UV radiation dosages onthe beach, the call is for highest protec-tion products (21) and additional shadingstrategies to avoid localized sunburns andsignificant suberythemal damage. In ad-dition, skin care active such as niacin-amide might help to reduce the harmfuldamage by protecting or by stimulatingintrinsic cellular repair mechanisms.A key driver for applying higher amountsof those high performance sunscreens

are pleasing sensory features. Most like-ly it is a sensory endpoint which tellsconsumers to stop applying more sun-screen at a certain optical or touch sen-sation (23). What improved sensory features can dofor the application amount shows astudy, in which we investigated the rightbalance of inorganic pigments and Poly-silicone-15 (PARSOL® SLX) by comparingthe voluntary use level in a consumerstudy. Participants received two sun-screens; one contained next to other UVfilters 6% Titanium Dioxide, the other amix of 3% Titanium Dioxide and 3%Polysilicone-15 (PARSOL® SLX). Both hadsimilar SPFs, 26 and 27 respectively. Theparticipants had to apply the test creamsto a defined skin area for 14 days andthereafter the weight of the used sun-screen was measured. It turned out thatthe sunscreen with a mix of TitaniumDioxide and Polysilicone-15 (PARSOL®SLX) was unconsciously used at a 29%higher level. This trial can be consideredas principal to demonstrate that appeal-ing sensory features can enhance the to-tal amount applied on the skin leadingto a better ultimate protection of sun-burn and of damages due to suberythe-mal UV exposure.Creating high broad spectrum perfor-mance and well accepted textures allur-ing for more product usage represents atough challenge for the formulator. Alloptions of the sunscreen formulation

tool box need to be considered. It startswith the right UV filter combinations fora maximized performance, an optimaluse level of non-oily, skin pleasing UVfilters like Phenylbenzimidazole Sulfon-ic Acid (PARSOL® HS), Polysilicone-15(PARSOL® SLX) and Titanium Dioxide(PARSOL® TX) and in addition the rightchoice of texture builders. The use of theemulsifier Potassium Cetyl Phosphate(AMPHISOL® K) especially ensures thestability of these complex emulsion sys-tems with relatively high oil loading andhigh content of pigments and UV filters.

■ Conclusions

Sunlight is a factor of setting good moodto people. It doesn’t wonder that thiscreates a sun seeking behavior, not justonly in holiday situations but also in ourdaily life, whenever the sun is shining.Unfortunately sunlight comes also witha downside, that can create significantaging and health effects, which call forprotective strategies. Avoidance of sun-burn turns out to be not enough to en-sure successful and sufficient protection.Dosages below sunburn can still affecthealth and beauty. For shorter exposuresa minimum of SPF 15 with an excellentUVA coverage and further protective in-gredients is recommended. Longer andsubsequent exposures, e.g. beach holi-days call for very high SPF numbers with

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broadspectrum coverage and additionalshade seeking strategies. The sensoryprofiles of those high performance for-mulas should be adapted to the con-sumer’s expectations driving the sunseekers to use plenty amount for a bet-ter ultimate UV protection. A reducedhealth risk and a long time young look-ing facial appearance are waiting as thereward.

AcknowledgementThe authors’ thank Rolf Schütz for a criti-cal review of the document.

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* Authors’ address:Dr. Jürgen Vollhardt

Anne JanssenChristine Saecker

DSM Nutritional Products Ltd.P.O. Box 2676

4002 BaselSwitzerland

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