introduction in a model cream (oil-in-water emulsion), containing a mixture of UVA and UVB fi lters. A small but statistically signifi cant decrease in BMDBM photodegradation was obtained when the UVA fi lter was encapsulated alone into the LMs (the extent of degradation was 28.6% ± 2.4 for nonencapsulated BMDBM and 26.0% ± 2.5 for BM- DBM-loaded microparticles). On the other hand, the co-loading of OCR in the LMs produced a more marked reduction in the light-induced decomposition of microencapsu- lated BMDBM (the UVA fi lter loss was 21.5% ± 2.2). Therefore, incorporation in LMs of BMDBM together with the sunscreen OCR is more effective in enhancing the UVA fi lter photostability than LMs loaded with BMDBM alone (16,80). INCORPORATION IN MESOPOROUS SILICA The effect of incorporating avobenzone (AVO/BMDBM), oxybenzone (OXY) and OMC in mesoporous silica (SBA-15) was investigated by Daneluti et al. Stick formulations containing “free” and “incorporated” UV fi lters (SF1 and SF2, respectively) were prepared. Different physicochemical analytical techniques including N2 adsorption isotherm, small-angle X-ray scattering, and thermogravimetry/derivative thermogravimetry (TG/ DTG) were used to confi rm that OMC had been successfully entrapped in SBA-15. Cutaneous delivery experiments using the porcine skin with quantifi cation by UHPLC- MS/MS demonstrated skin deposition of avobenzone and oxybenzone after different ap- plication times (6, 12, and 24 h). The amounts of OMC and AVO permeated across the porcine skin were below the limit of quantifi cation of the UHPLC-MS/MS method (i.e., concentrations 10 ng mL-1) for application times of 6 and 12 h. However, after applica- tion for 24 h, both UV fi lters were detected in the receiver compartment, and permeation from SF1 and SF2 was not signifi cantly different at 24 h. Regarding the OXY results, this was detected in the receiver compartment after application for 6, 12, and 24 h for both SF1 and SF2 although transdermal permeation from both formulations was signifi - cantly lower at each time point with SF2: SF2 having a 30-, 12-, and 1.5-fold lower OXY permeation than SF1 after 6, 12, and 24 h, respectively. OXY showed the highest capac- ity to permeate the skin at all exposure times. After 24 h, the OXY amount detected in the receptor compartment after application of SF1 was 18.7-fold and 21.5-fold greater than that of AVO and OMC, respectively, whereas for SF2, it was 33-fold and 16.5-fold greater than that of AVO and OMC, respectively. OXY has a slightly lower molecular weight (228.25 g mol-1) than OMC and AVO, but more importantly, it is less lipophilic (log Ko/w 3.79 vs. 5.96 and 4.51, for OMC and AVO, respectively), and this may facilitate partitioning into the viable epidermis and hence transdermal permeation (81). DISC USSION Exte nsive research on the tests used for estimating the permeation behavior of various groups of UV fi lters has been carried out. This has led to the discovery of safe vehicle systems that prevent skin absorption of effi cacious UV fi lters and the development of advanced ones with high photostability and low toxicity. Lipi d carriers seem to be a good alternative to formulate chemical UV fi lters reducing their skin penetration while maintaining good photo-protective abilities. Nano particles seem to be interesting carriers of sunscreen, as demonstrated by the good stability, lower toxicity, lack of phototoxic effect in cells, and no allergic reaction in mice. DISTRIBUTION OF UV FILTERS ON THE SKIN 319

In addition these particles, because of their crystallinity, can scatter/refl ect incoming UV radiation, increasing the sun protection factor. A be nefi cial characteristic of NPSUNs is their high skin substantivity which could min- imize the need for repetitive applications. Such a characteristic, along with the factor of non-penetrability, makes NPSUNs highly applicable. More over, incorporation in LMs of combination of sunscreen substances is signifi cantly effective in enhancing the UVA fi lter photostability. SBA- 15, an innovative mesoporous material, increased photoprotection by UV fi lters while reducing their cutaneous penetration and transdermal permeation. Mesoporous silica materials of type SBA-15 are nontoxic and biocompatible, and the presence of an ordered pore network with homogeneous pore size enables a good and reproducible con- trol of drug loading and a benefi cial release profi le. Furthermore, the high pore volume and large surface area facilitate drug loading and drug adsorption. Cons equently, a development of formulas based on non-penetrating photo protectors is considered to be more than relevant. This explains why the biggest challenge cosmetolo- gists face is the development of appropriate products that could hinder skin penetration. ACKN OWLEDGMENTS This article is a literature review completed in the frame of research undertaken in Labo- ratory of Chemistry-Biochemistry-Cosmetic Science, Division of Aesthetics and Cosmetic Science, Department of Biomedical Sciences, the University of West Attica (Egaleo, Greece), supported by an Academic Scholarship. Assistance with useful data and con- structive recommendations was provided by colleagues of the Section of Pharmaceutical Technology, Department of Pharmacy, School of Health Sciences, National and Kapodis- trian University of Athens. DECL A RATION OF INTEREST The authors have no declaration of interest. The authors alone are responsible for the content and writing of the manuscript. REFE RENCES (1) P . Pavlou, M. Rallis, G. Deliconstantinos, G. Papaioannou, and S. Grando, In-vivo data on the infl u- ence of tobacco smoke and UV light on murine skin, Toxicol. Ind. Health, 25(5), 231–239 (2009). (2) M . Schlumpf, P. Schmid, S. Durrer, M. Conscience, K. Maerkel, M. Henseler, M. Gruetter, I. Herzog, S. Reolon, R. Ceccatelli, O. Faass, E. Stutz, H. Jarry, W. Wuttke, and W. Lichtensteiger, Endocrine activity and developmental toxicity of cosmetic UV fi lters - an update, Toxicology, 205(1-2), 113–122 (2004). (3) S . T. Butt and T. Christensen, Toxicity and phototoxicity of chemical sun fi lters. Radiat. Prot. Dosimet., 91(1-3), 283–286 (2009). (4) K . M. Hanson, E. Gratton, and C. J. Bardeen, Sunscreen enhancement of UV-induced reactive oxygen species in the skin. Free Radic. Biol. Med., 41(8), 1205–1212 (2006). (5) J . F. Nash and P. R. Tanner, Relevance of UV fi lter/sunscreen product photostability to human safety. Photodermatol. Photoimmunol. Photomed., 30, 88–95 (2014). (6) J . V. Freitas, N. P. Lopes, and L. R. Gaspar, Photostability evaluation of fi ve UV-fi lters, trans-resveratrol and beta-carotene in sunscreens, Eur. J. Pharm. Sci., 78, 79–89 (2015). JOURNAL OF COSMETIC SCIENCE 320