Interaction of sunscreen TiO 2 nanoparticles with skin and UV light: penetration, protection, phototoxicity Alexey Popov *a,b , Jürgen Lademann c , Alexander Priezzhev b , and Risto Myllylä a a Optoelectronics and Measurement Techniques Laboratory, Faculty of Technology, University of Oulu, P.O. Box 4500, FI-90014, Oulu, Finland; b International Laser Center, Lomonosov Moscow State University, Moscow, 119991, Russia; c Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Medical Faculty Charité, Humboldt University Berlin, Berlin, Germany ABSTRACT Titanium dioxide (TiO 2 ) nanoparticles are extensively used nowadays in sunscreens as protective compounds for human skin from UV radiation. In this paper, such particles are investigated from the viewpoint of penetration into living skin, UV protective properties (compared with silicon (Si) particles) and as sources of free radicals if UV-irradiated. We show that: a) even after multiple applications, the particles are located within the uppermost 3-μm-thick part of the skin; b) the optimal sizes are found to be 62 nm and 55 nm, respectively for TiO 2 and Si particles for 310-nm light and, correspondingly, 122 and 70 nm – for 400-nm radiation; c) if applied onto glass, small particles of 25 nm in diameter produce an increased amount of free radicals compared to the larger ones of 400 nm in diameter and placebo itself; however, if applied onto porcine skin in vitro, there is no statistically distinct difference in the amount of radicals generated by the two kinds of particles on skin and by the skin itself. This proves that although particles as part of sunscreens produce free radicals, the effect is negligible in comparison to the production of radicals by skin in vitro. Keywords: Nanoparticles, UV light, skin, sunscreen, phototoxicity 1. INTRODUCTION Due to depletion of ozone because of human industrial activity resulting in the decrease of the ozone layer, from one side, and increasing desire of people to stay outdoors during holidays, additional protection (to what is provided by skin) is required. That is the main purpose of sunscreens use. Protective properties of sunscreens are caused by absorption and scattering by their ingredients, chemical and physical components. 1 Chemical components are organic molecules absorbing UV light. Physical components are mineral insoluble nanoparticles having both absorbing and scattering properties. During recent years great concerns have been raised about the effect of nanoparticles used in sunscreens on human health. Among them are the fears about particle penetration into viable layers of skin through stratum corneum after multiple applications of sunscreens onto body surface. Because of small particle sizes (at a range of tens of nanometers) these concerns are not groundless. Size also matters if UV protection is considered: not all the sizes are equally attenuating. The third issue we present here is comparison between amounts of free radical generated by nanoparticles and skin under UV irradiation. * popov@ee.oulu.fi , dwelle@rambler.ru ; phone 358 8 553-2760; fax 358 8 553-2774; www.ee.oulu.fi/~popov Clinical and Biomedical Spectroscopy, edited by Irene Georgakoudi, Jürgen Popp, Katarina Svanberg, Proc. of SPIE-OSA Biomedical Optics, SPIE Vol. 7368, 736822 · © 2009 SPIE-OSA CCC code: 1605-7422/09/$18 · doi: 10.1117/12.831573 SPIE-OSA/ Vol. 7368 736822-1 Downloaded from SPIE Digital Library on 12 Feb 2010 to 66.165.46.178. Terms of Use: http://spiedl.org/terms