A Noninvasive Objective Measure of Sunscreen Use and Reapplication

Abstract

Objectives: To study whether a noninvasive swabbing technique can detect sunscreen use for up to 6 hours, and whether the technique can detect reapplication of sunscreen. Methods: Thirty volunteer office workers were randomly assigned to have one of a variety of sunscreens applied using recommended application techniques, and half were randomly assigned to have sunscreen reapplied after 3 hours. Alcohol-based swabs were used to obtain a sample from participants' arm at 20 minutes, and hourly from 1 to 6 hours post-application. Absorption readings were analyzed using an UV-visible spectrophotometer. Results: The swabbing technique was consistently able to distinguish the sunscreen from control swabs for up to 6 hours. The absorption readings between 20 minutes and 6 hours were significantly higher than control swabs. There were no differences between the group that had sunscreen reapplied and the group that did not. Conclusion: The sunscreen swabbing technique is an effective noninvasive method for detecting a variety of sunscreen products in adults over a 6-hour period. No differences in absorption readings were found with sunscreen reapplication. This procedure will be a useful adjunct to other objective measures of sun protection and UV radiation exposure, resulting in a more accurate picture of the sun protection habits of individuals. (Cancer Epidemiol Biomarkers Prev 2005;14(3):722 -6)

Validity of Beachgoers' Self-report of Their Sun Habits

“…12,13 We used 70% isopropyl alcohol swabs (BD Alcohol Swabs; BD, Franklin Lakes, NJ) because they are individually wrapped and small (approximately 2.5 cm 2 ) and have been used previously. 13 Participants' skin was swabbed at 4 anatomical sites: 1 baseline site (underarm) to provide a skin swab with no sunscreen and 3 potential sunscreen sites (forearm, cheek, and thigh). Staff (K.B.L.…”

“…Sunscreen absorbance readings obtained from swab samples were assessed at 320 nm because this wavelength has been previously reported as a reliable indicator of sunscreen use. 12,13 A cutoff at an absorbance of 0.147 has been used within a controlled environment (office setting), where sunscreen was applied at a recommended dose, to classify a swab as either sunscreen positive or sunscreen negative, with a sensitivity of 99.7% and a specificity of 96.7%. 13 It was hypothesized that in an outdoor environment, the cutoff at a wavelength of 320 nm may need to be adjusted to account for self-application of sunscreen, water, and sand abrasion.…”

“…12,13 A cutoff at an absorbance of 0.147 has been used within a controlled environment (office setting), where sunscreen was applied at a recommended dose, to classify a swab as either sunscreen positive or sunscreen negative, with a sensitivity of 99.7% and a specificity of 96.7%. 13 It was hypothesized that in an outdoor environment, the cutoff at a wavelength of 320 nm may need to be adjusted to account for self-application of sunscreen, water, and sand abrasion. 13 Based on participant self-report with full disclosure of the swabbing procedure, agreement between swabs taken from this beach population and participant selfreport was also highest in the same range (0.140-0.147).…”

“…13 It was hypothesized that in an outdoor environment, the cutoff at a wavelength of 320 nm may need to be adjusted to account for self-application of sunscreen, water, and sand abrasion. 13 Based on participant self-report with full disclosure of the swabbing procedure, agreement between swabs taken from this beach population and participant selfreport was also highest in the same range (0.140-0.147). As a result, any adjustment seemed unwarranted.…”

“…12 This procedure is based on the fact that organic sunscreens are soluble in a range of organic solvents, which are specifically designed to absorb radiation in the UV spectrum. 12 Sunscreen swabbing has proved successful within laboratory 12 and office 13 settings and on a small sample of children aged 2 to 4 years at a child care center. 12 It is portable, rapid, and easy to perform, and swabs can be stored and analyzed in batches days or weeks later.…”