the measurement of the sun protection factor (SPF) is usual method in the examination of the effectiveness of a sunscreen. Some studies have shown the large variability of several factors in a study affects the SPF and it is to be expected that
the
photoprotection afforded by a sunscreen will also depend upon the topical amount of a sunscreen applied. The purpose of this study is to investigate the relationship between the SPF and topical amounts of a sunscreen by phototesitng on 23 healthy
male
subjects on the third decade of age not exhibiting any abnormal sensitivity to sunlight.
@ES The results are summarized as follows:
@EN 1. The 85 homomenthyl salicylate lotion, which is used as a control in the measuremaent of the SPF, was applied in 1cm2 of skin with 5 different amounts of 1mg, 1.5mg, 2mg, 3mh, 4,g, and ultraviolet light with the 4-fold dose of each
subject's
MED
was irradiated. On the evaluation with the colorimeter 24 hours after the irradiation, the degree of erythema decreased as the topical amount was increased. The minimal erythema was noted at the amount of 2mg/cm2 and we ascertained that 2mg/cm2
is
the
adequate amount in the measurement of SPF.
2. The 3.755 titanium dioxide and aluminum hydroxide lotion was appled in 1 cm2 of skin with the amounts of 2mg, which is standardized by FDA, and with the decreased amounts of 1mg, 0.5mg, the SPF decreased significantly from 7.4±2.7 at the
amount of
2mg/cm2 to 4.2±1.5 ant 1mg/cm2, and 2.4±0.3 at 0.5mg/cm2.
3. With the 12% titanium ixide foundation, which was applied with the same amounts as 2., the SPF was 13.5±6.7 at the amount of 2mg/cm2 and decreased significantly to 4.9±2.1 and 3.0±1.0 as the topical amount was decreased to 1mg/cm2
respectively.
From the above results we conclude that the topical amount of a sunscreen affects the degree of photoprotection significantly and the SPF decrease signincantly as the topical amounts are decreased below the 2mg/cm2, which is standardized by FDA.
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