Sun protection factor analysis of sunscreens containing titanium dioxide nanoparticles

The effect of micronization on sun protection factor (SPF) were tested on two types of titanium dioxide (TiO2) with primary particle sizes of 20 nm and 170 nm. Oil/water creams with 5%, 10%, and 20% concentrations of each type of TiO2 were prepared, and SPF was measured using both in vitro and in vivo methods. In vitro analysis demonstrated that submicron-sized TiO2 cream had a lower SPF value than nanosized TiO2 formulations of the same concentration. In vivo experiments confirmed this result, and a strong correlation between in vitro and in vivo measurements was observed. Furthermore, the SPF values of nanosized TiO2 sunscreen were concentration-dependent in the range of 5% to 20%. Scanning electron microscopy results indicate that the higher SPF of nanosized TiO2 formulations may be due to the formation of multilayer agglomerates by small particles at nano-scales, leading to a reduced void space between particles and a more efficient barrier to protect skin from sunlight.