The diffusion of BP-3 acros s excised pig-ear skin was studied using a static diffusion cell based on the Franz design and analyzed by HPLC. Results indicated the nanoparticles’ ability to limit sunscreen absorption. Moreover, nanoparticles with a low degree of sub- stitution provided the highest amounts of BP-3 in the receiver compartment. Among these, nanoparticles with short chain length provided higher amounts of BP-3 than nanoparticles with high chain length. There was a correlation between the size of the nanoparticles and the fractional amount of BP-3 recovered in the skin 6 h after topical application: the amount of BP-3 decreased with increasing substitution degree and, for each degree of substitution, increasing nanoparticles size. This indicated the ability of low-substituted formulations to enhance the location of sunscreen in the epidermis, achieving high protection (79). CYCLODEXTRIN DERIVATIVES Th e interaction between 4-M BC and hydrophilic α-, β-, and γ-cyclodextrin derivatives was investigated in water by phase-solubility analysis. Among the studied cyclodextrins, random methyl-β-cyclodextrin (RM-β-CD) had the greatest solubilizing activity. The light-induced decomposition of 4-MBC, in emulsion vehicles, was markedly decreased by complexation with RM-β-CD. The infl uence of RM-β-CD on human skin penetration of the sunscreen was investigated in vivo, using the tape-stripping method. Considerable quantities (21.2–25.1% of the applied dose) of 4-MBC permeated in the SC. However, no signifi cant differences in the amounts of UV fi lter in the 10 fi rst strips of the horny layer were observed, between the formulations containing 4-MBC free or complexed with RM- β-CD. Therefore, RM-β-CD complexation did not alter the retention of 4-MBC in the superfi cial layers of the SC, where its action is more desirable (18). So the complexation with RM beta CD seems to be not effective. COMBINATION OF ORGANIC UV FILTERS Coz zi et al. carried out an investiga tion and made a comparison on how sunscreen formu- lations (whether free or encapsulated) with the common combination of organic UV fi l- ters, BMDBM and OCR, behave. This comparison was made concerning photostability, skin penetration, and retention on the surface of the skin. UV fi lters were enclosed in sol–gel silica glass microcapsules. Free and encapsulated UV fi lters were incorporated in a water-based cold lotion divided into three preparations: formulation without actives (F1), formulation containing UV fi lters (BMDBM 3% and OCR 9%) in free form (F2), and formulation F3 containing encapsulated UV fi lters. To examine the UV fi lter perme- ation in the SC and their retention on the skin surface, the Fourier transform infrared spectroscopy (FTIR) imaging spectroscopy and attenuated total refl ection Fourier trans- form infrared spectroscopy techniques were applied. Skin samples were treated with 2 mg/c m2 of sunscreen formulations applied topically with 1 min of massage to cover the entire skin surface uniformly and mounted in diffusion Franz cell system. The skin samples were maintained in this condition for 2 h for the pen- etration measurement and during 4 h for the retention measurement on the skin surface. At the end of the 2-h treatment, the skin samples were removed from the diffusion cells, and the sunscreen remaining on the skin surface was gently removed before analysis. The tape- stripping technique was used. DISTRIBUTION OF UV FILTERS ON THE SKIN 317

The technique of FTIR imaging, in combi nation with a tape-stripping procedure, gives the opportunity to picture and compare the UV fi lter permeation of a specifi c sunscreen product in the SC. A different penetration behavior for the BMDBM between the traditional sunscreen formulation and the sunscreen formulation based on encapsulation technology was detected. With the regular formulation, the UV fi lters presented not only a high concentration on the skin surface as expected but also a signifi cant concentration deep inside the SC, indicating the BMDBM under “free” formulation did not remain on the skin surface but penetrated deep inside the skin. UV fi lters were detected up to the layer six under free formulation after just one single topical application. On the other hand, the same UV fi lters combined with encapsulation technology were observed on the skin surface, and almost no penetration was detected inside the SC. Encapsulated BMDBM (avobenzone) was not detected after the layer one, clearly indicating that the encapsulation technology allowed to keep the UV fi lters at the surface of the skin where they will exert their pur- pose most effi ciently (69) (see Figure 3). Microparticles loaded with BMDBM or wit h combined BMDBM and OCR were pro- duced by the hot emulsion technique, using glyceryl behenate as the lipid material and poloxamer 188 as the surfactant. The LMs were characterized by release studies, scanning electron microscopy, and powder X-ray diffractometry. The BMDBM and OCR loading was 15.2 and 10.6%, respectively. To reproduce the conditions prevalent in commercial sunscreen products, the photo-protective effi cacy of the LMs was evaluated after their Figure 3. FTIR images allow to visualize and compare the BMDBM penetration inside the SC for different skin samples: skin samples treated with formulations F1, F2, and F3 compared with the untreated skin. For each sample, the FTIR images were scanned before (control), after topical application on the sunscreen for- mulation, and after eight sequential tape strips [Cozzi et al. (69)]. JOURNAL OF COSMETIC SCIENCE 318