Comparison of dermal absorption of zinc from different sunscreen formulations and differing UV exposure based on stable isotope tracing.
In a pilot study to determine if zinc (Zn) from zinc oxide nanoparticles in sunscreen can penetrate human skin in vivo, nanoparticles (~30nm) of a stable isotope (52% (68)Zn enrichment) were incorporated into an essentially phytochemical-based formulation and applied to the backs of 3 human subjects twice daily for 5 days during the Southern Hemisphere winter. Blood and urine were collected prior to application and at regular intervals and up to 50 days. As observed in a larger outdoor trial following this pilot study but with a different formulation and with UV exposure: values of (68)Zn in blood continued to increase beyond the 5 day application phase with the highest measurement at 14 days after the first application; variable amounts of the (68)Zn tracer were observed in urine; and the amounts of extra Zn added to blood were small and indicate very low levels of absorption (minimal estimate <0.01% of the applied dose) through the skin. Reasons for differences in absorption detected in the stable isotope trials and previous investigations include: the sensitivity of the stable isotope method; the duration of the investigations; the number of applications of sunscreen formulation; in vitro methods with excised skin; lack of measurement of blood and urine; no skin flexing; and lack of UV exposure.
Graduate School of the Environment, Macquarie University, North Ryde NSW 2109, Australia. brian.gulson@mq.edu.au
Brian
B
Gulson
Herbert
H
Wong
Michael
M
Korsch
Laura
L
Gomez
Philip
P
Casey
Maxine
M
McCall
Malcolm
M
McCulloch
Julie
J
Trotter
Jenny
J
Stauber
Gavin
G
Greenoak
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053758:Nanoparticles; D010865:Pilot Projects; D012867:Skin / Q000378:metabolism; D012869:Skin Absorption; D013473:Sunscreening Agents / Q000008:administration & dosage / Q000378:metabolism*; D014466:Ultraviolet Rays; D015032:Zinc / Q000008:administration & dosage / Q000378:metabolism* / Q000652:urine; D015033:Zinc Isotopes / Q000008:administration & dosage / Q000378:metabolism / Q000652:urine; D015034:Zinc Oxide / Q000008:administration & dosage / Q000378:metabolism*
D013473:Sunscreening Agents; D015033:Zinc Isotopes; D015032:Zinc; D015034:Zinc Oxide