Objective To assess the protective effect of low-dose sunscreen and different applying methods, and provide a scientific basis for guiding customer sunscreen usage.
Methods A total of 60 subjects were randomly divided into control group and sunscreen group. The sunscreen group applied sunscreen at a low dose (0.5mg/cm2) on the back of hands and the control group did not. In addition, the sunscreen group was treated with spreading sunscreen twice and six times over a day on the back of left hand and right hand respectively. The subjects were exposed to sunlight for six hours per day (8:00-11:00, 14:00-17:00) during nine continuous days of military training. The skin color changes induced by sunlight exposure were evaluated in the volunteers with a tristimulus colorimeter.
Results Both groups showed reduced lightness (L) (after:53.95-54.86, before:56.75-58.64) (P < 0.05) as well as increased green-red saturation (a) (after:10.86-11.59, before:9.44-10.20) and blue-yellow saturation (b) (after:20.31-21.09, before:19.16-19.74) (P < 0.05) after sunlight exposure. The color differences (△ E) of left and right hands in the sunscreen group (left:3.31±1.91, right:3.17±1.82) were lower than those in the control group (left:5.63±2.37, right:5.74±2.56) (Ps < 0.05), and no difference was observed between the hands treated with twice and six times of sunscreen (P>0.05).
Conclusion Using low-dose sunscreen can only slow down but cannot avoid the change of skin color to black, red, and yellow compared to using no sunscreen products. In the case of using low-dose sunscreen, increasing application times does not enhance its protective effect.
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