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Water‐resistant sunscreens for skin protection: an in vivo approach to the two sources of sunscreen failure to maintain UV protection on consumer skin
Author(s) -
Puccetti G.
Publication year - 2015
Publication title -
international journal of cosmetic science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 62
eISSN - 1468-2494
pISSN - 0142-5463
DOI - 10.1111/ics.12238
Subject(s) - tap water , surface tension , absorption of water , water resistance , diffusion , chemistry , sun protection , surface water , materials science , chemical engineering , environmental chemistry , environmental science , composite material , environmental engineering , physics , dermatology , engineering , medicine , quantum mechanics , thermodynamics
Synopsis Objectives The water resistance of sunscreen products has taken more importance for the UV protection of consumers involved in water activities and sports. The present work introduces a new in vivo approach to measure the water resistance of sunscreens on the actual skin of subjects, which can be easily applied to salt, chlorine and tap waters. The stress sources of sunscreen films on skin originate from two phenomena: high surface tension stress as the skin transits through the air/water interface and water diffusion into the film immersed in bulk water. Methods The water resistance of sunscreen products is measured on the forearms of subjects by means of a new layered water bath approach that physically separates both stresses. Tape strips are subsequently taken and analysed for UV ‐A and UV ‐B optical densities via (1) imaging for remaining filters and (2) in vitro SPF absorption spectra. Results Water‐resistant sunscreens generally perform well when immersed in bulk water even subjected to agitation, but they show a wide range of performances when considering their behaviour at the air/water interface. The differences are more pronounced in salt water than tap water. Conclusions The results confirm 2 stress origins in sunscreen exposure to water: interfacial surface tension and bulk water diffusion. Polymers bring improvements to the resistance of sunscreens to bulk water but show wide latitude in performances when subject to the water surface tension stress. Globally, a higher loss of filters is observed in the UV ‐A than in the UV ‐B, which is attributed to more UV ‐A filter loss or degradation and thus resulting in a decreased protection in the UV ‐A.