Development of actinic lentigines due to multiple sub‐erythemal exposure to UVA1 radiation in Asian skin

The appearance of actinic lentigines mainly found on face, back of the hands, upper back and décolleté is associated with chronic sun exposure. However, there is no study looking at the role of long UVA specifically in the development of actinic lentigines. This study was conducted in 20 Japanese adult women exposed on the upper back area three times per week for 6 weeks to incremental sub‐erythemal UVA1 doses (5 J/cm2 at weeks 1 and 2, 10 J/cm2 at weeks 3 and 4 and 15 J/cm2 at weeks 5 and 6). Clinical assessment, performed on day 0 (before any exposure), and on days 14, 28 and 42, included the evaluation of skin pigmentation (pigmented spots), chromametry of the pigmented skin lesions and measurement of dyschromy. The number of pigmented spots and uniformity of the skin's pigmentation were clearly increased in comparison with baseline, statistical significance of the difference (p < 0.05) being reached at D 28 and D 42 in both cases. In conclusion, repeated sub‐erythemal UVA1 exposure induces the development of actinic lentigines. Thus, a suitable protection including long UVA coverage is also needed to prevent from the damages induced by low, sub‐erythemal doses of UV exposure.

Clinical assessment was to be performed on day 0 (before any exposure), and on days 14, 28 and 42, using a lesion positioning mask to enable reproducibility of the measurements from visit to visit, by (i) the clinical evaluation of skin pigmentation (pigmented spots) using a 10 cm visual analogic scale (VAS), 4 (0 = absence of spots; 10 = most numerous spots), (ii) chromametry (Minolta chromameter,Japan)ofthepigmentedskinlesions(oneareawithaspot) andofnormalskin(oneareawithoutspot),(iii)measurementofdy-schromyusinga0-6photonumericscale. 5 The subjects had to sign an informed consent form prior to enrolment.The study protocol wassubmittedtoandapprovedbyanEthicalCommittee(Nikoderm Research,Osaka,Japan).

| RE SULTS
Repetitive irradiation with sub-erythemal UVA1 doses had little effect on skin colour changes assessed by objective instrumental measurementsusingachromameter,eitherinareaswithpigmentation spot or areas without spot (Chromametry results are provided in Table A1).

| CON CLUS I ON S AND PER S PEC TIVE S
Repetitiveirradiationwithsub-erythemallongwaveUVAdosesis associatedwithdevelopingactiniclentiginesintheupperbackof adult Asian women.It is noteworthy that a UVA1 dose of 15 J/ cm 2 is a dose that can be received easily during a spring or a sum-merdayinJapanbyanindoorworker. 6 Reactive Oxygen Species (ROS), leading to subsequent oxidative damagetocellularcomponentssuchasDNA,lipidsandproteins.

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in all cutaneous layers.Hyperpigmentation of the skin is one of the main dermatological concerns for populations with pigmented skin phototypes and ishighlyprevalentinAsiaandIndia.Ofthemostcommonhyperpigmentationdisorders,actiniclentiginesareconsideredasphotoaging lesions only observed on sun-exposed areas.After adjustment for age,sexandskintype,solarlentiginesonthebackwereshowntobe positivelyassociatedwithcumulativeandintermittentsunexposure, aswellaswithahistoryofsunburnsbeforetheageof20 yearsand the number of sunburns in childhood. 3QUE S TION ADDRE SS ED Thepresentworkwascarriedouttoinvestigatewhetherrepeated, butsub-erythemalUVA1exposureisalsoassociatedwiththedevelopment of actinic lentigines in the upper back of adult Asian women.
By contrast, irradiations of the upper back area with suberythemal UVA1 doses had clear effects on pigmentation and dyschromy.This is illustrated in a representative photograph of aUVA1exposedspottakenundernormalandUVlightprovided hereafter.Pigmentation and dyschromy results are summarized in Table 1: a statisticalanalysis(Onesamplet-Test) of the change from baseline was performed.The relative mean difference (%) between values obtained at D14, D28 and D42 in comparison with baseline were calculated along with p-values for the difference.Thenumberofpigmentedspotsasquantifiedbythe0-10VAS (Figure 1, Pigmentation) and uniformity of the skin's pigmentation asquantifiedbythe0-6photonumericscale(Figure 1,Dyschromy) wereclearlyincreasedincomparisonwithbaseline,statisticalsignificance of the difference (p < 0.05)beingreachedatD28andD42 inbothcases.Ofnote,sucheffectsonpigmentationanddyschromy were not associated with symptoms such as itch or inflammation, sincenoneofthesubjectsreportedanysignsinrelationtotheUVA1 doses administered at any time.
consequences such as hyperpigmentation, inflammation, photo-immunosuppression, sun allergies, photoaging and photocancers.The persistence of solar lentigines over time following cessation of the irradiations was not investigated in this study and it is recognized that this is certainly a limitation ofthestudywithonly42 daysoffollow-upinsubjectsexposedto theUVA1irradiations.Howeverinanycase,thepresentinvestigations highlight the need for suitable sunscreen protection against damages caused by UVA1 irradiation.This is necessary not only under cumulative and intermittent sun exposure conditions or in subjects with a history of sunburns but also under low, suberythemal doses of UV exposure.AUTH O R CO NTR I B UTI O N AkimichiMoritawasinvolvedinconceptualization,projectadministration,supervision,writing-reviewandediting,datacuration,formalanalysis,investigationvisualization.SophieSeitéwasinvolvedin conceptualisation,validationandfundingacquisition.GuenaelleLe Dantec was involved in methodology.Delphine Kerob was involved indatacuration,medicalwritingreviewandeditingandvisualization.Allauthors(AM,SS,GLDandDK)havereadandapprovedthefinal manuscript.ACK N O WLE D G E M ENTS This study was funded by La Roche-Posay Laboratoire Dermatologique.TheauthorsacknowledgeDanielCaveyforeditorialand medical writing assistance.CO N FLI C T O F I NTE R E S T S TATE M E NT S.Seité, G.Le Dantec and D.Kerob are full time employees of La Roche-Posay.
Indeed,theprotocolwas designed to reach this dose progressively during the 6 weeks of study.As reviewed by Bernerd et al., 7 UVA1 rays generate Note: Delta %: relative mean difference (%) in comparison with baseline.Abbreviation:SD,standarddeviation.