Abstract
To establish an in vitro method for measuring SPF with a high correlaion to in vivo SPF, it is important to understand all he biological phenomena and effects in terms of the eryhemal response o UV light. Our research focuses on the problem of he synergisic effect of UVA on the biological acivity of UVB. We invesrtigated the UVA-promoter action using spectroradiometric measurement of the UV transmittance with and without the sunscreen applied and in vivo SPF values presented in the Federal Register OTC Monograph (1978). We analyzed the effective intensity by multiplying the transmitted UV spectrum of sunscreens by the biological effectiveness for the erythemal action spectrum, estimating the transmitted UVA of sunscreens, and confirmed the UVA photoaugmentative effect related to the erythemal response. We also confirmed that this photoaugmentative effect is affected by the UVA/UVB ratio in relation to the synergy between UVA and UVB. When we applied the equations obained form these results to various sunscrees, we obtained a very high correlation with the in vivo SPF values. In addition, by using the correlation obtained form these equations, we have been able, for the first time, clearly determine the regions where the erythemal response related reciprocity does and does not apply. The occurrence of a non-reciprocity region where reciprocity does no apply, suggests the other biological factors are important. We can forecast SPF values up to the high-SPF region at much higher accuracy than achieved previously by using the SPF equations while taking these unclarified biological factors into account.
