Penetration test through the SC of pig skin was carried out using SLN and NLC containing Nile red as a marker. Nile red-loaded SLN and NLC (0.005% w/w) were prepared as described before, incorporating the dye in the melted lipid phase. Skin excised from pig ears was mounted in Franz diffusion cells containing phosphate buffer pH 7.4 as receptor solution, and the surface of the skin was treated with 1 mL sample of Nile red-loaded SLN or NLC dispersion. The Franz diffusion cells were kept in a water bath at 37 ̊C and, after 2 h contact, the remaining formulation was removed and tape stripping was performed on the skin. Fifteen tapes (Scotch® packaging tape) of 2 × 2 cm were used, weighting each tape before and after skin application. Nile red was extracted from the tapes, stirring with a volume of methanol during 24 h. Tapes 1 to 5 were extracted individually and subsequent tapes were extracted in clusters (6 - 10 and 11 - 15). The extracts were filtered and Nile red was quantified by spectrophotometry UV/Vis (λ = 555 nm) (Varian Cary® 50 UV-Vis spectrophotometer, Australia). Penetration distance was determined from tapes weight data, using Equation (3):