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Phototoxicity of bergamot oil in solar simulating radiation (SSR ≥ 290 nm) and in long ultraviolet radiation (LUV ≥ 320 nm) has been compared by studying photoaugmentation of erythema in the guinea pig after 24 h and pigmentary photoaugmentation in man on the 8th day. The results show that a close relationship exists between guinea pig and human responses, with both radiations used, and that man seems to be slightly more sensitive to phototoxic effects of bergamot oil than the guinea pig. This difference of sensitivity necessarily implies the participation of U VA (320–400 nm) in the phototoxic reaction of bergamot oil with solar radiation. This UVA participation is particularly obvious in the guinea pig; in man, the results are less clear and a certain synergy of UVB rays (290–320 nm) may be involved in the phototoxic UVA-induced reaction of bergamot oil. Despite these slight differences, the erythematous reaction in the guinea pig appears to be a remarkable experimental model to show out potential phototoxic reactions of products containing psoralens in man.

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SynopsisAprks avoir rappelk brikvement lc spectre d'action biologique du rayonnement ultraviolet du soleil sur la peau normale et les donndes thkoriques de protection qui en dicoulent, le caract& privisionnel de diff6rentes mkthodes d'6tude in vitro et in viuo des antisolaires est comment6 1 partir dc rksultats obtcnus en lahoratoire sur differents principes actifs (PABA, F:usolcx 4360, Giv Tan I:), ct prdparations cosm6tiques du commerce.Les mdthodes in vitro, basks sur I'absorption dans 1'UV des produits, aboutissent i une protection sur6valude et dans ces conditions B une extrapolation trds al6atoirc du pouvoir de protection.La m6thode utilis6c in vivo (ddterniination classique d'un indice de protection) souligne, dans le cadre de la prkdiction, le choix de la qualite d'absorption du fitre, de la source UV utilisbe, mais aussi de nombreus autres facteurs agissant sur la protection. Dans ces conditions, les rdsultats obtcnus chez Ie cobaye et l'homme avcc des irradiations simulant le spectre solaire, niontrent alors unc concordance satisfaisante pour les principes actifs 6tudibs. Ces observations sont ensuite commentkes par comparaison i d'autres travaux publiks faisant mention d'autre source d'irradiation (spectre de raies) et de methode de detection (therrnombtriquc cn particulier). Predictive nature of laboratory methods in sunscreen studies Summary After a brief summary of biological actions of UV radiation in sunlight on normal skin and the resulting theoretical claims of protcction, the different in viiro and i n . viuo methods of studies of sunscreens arc revic~ed. Laboratory results are given for different active substances: paraamino benzoic acid (PABA), 2 hydro4methoxy benzophenone and 2 ethoxy ethyl p-niethoxycinnamate, and a number of commercial preparations.Most in viiro methods are spectrophotonietric and dependence on them seems logical since the efficiency of sunscreens depends on a selective absorption of UV. The calculated sun protection factor (SPF) based on them is, however, always exaggerated. They also do not takc into account product interactions with normal skin, thickness of applied f i l m , product resistance to water nor the synergistic action of UV-A on the erythematous reaction of UV-B. This renders these methods of limited value and their extrapolation to an SPF is hazardous. The in viuo determination of SPF (multiplication factor of the time of natural photoprotection) used is based on the comparison of W irradiated 0142-5463/82/0800-0115 $02.00 0 1982 International Journal of Cosmetic Science 115 116 J. Girard et al. skin protected and unprotected with the sunscreen product using an objective method of measurement of erythema.Comparison of results on man and guinea-pig using a solar simulation give good agreement for the three materials studied and refcrence is made to other irradiating spectra and methods of determination of erythema, notably thermometric.The method described appears to be readily extrapolable to man and conveniently and rapidly applicable to cosmetic formulati...