During these ten years

During these ten years, most people love to expose their body to the sun, for example a Caucasian people like to walk along the beach have used with inorganic sunscreens widely. This is because of their safety and effectiveness, especially in blocking Ultraviolet sunlight, and the concern due to potential bad effects of organic sunscreens. The inorganic sunscreens are usually viewed as harmless colours that cannot enter the skin and are mostly unaffected by light energy as if organic sunscreens may be. The two most commonly used inorganic sunscreens are titanium dioxide (TiO2) and zinc oxide (ZnO). Although these two metal oxides have a difference in the UV spectrum, they share some general properties that are discussed briefly.
ZnO and TiO2, exist as odourless white powders made up of a Gaussian or normal distribution of particle sizes. Both of inorganic sunscreens have a few advantages (e.g. photostability and low photoallergic reaction rate) over organic UV ?lters, such as avobenzone. The earlier generations of inorganic sunscreen agents made up of large particles, producing an opaque (light blocking) and white appearance on the skin. In addition, the widespread adoption of early formulations containing TiO2 or ZnO was further slowed down by their poor dispersive properties and large particle size, which resulted in grainy and occlusive qualities.
For further improvement of the problem regarding the large size of a particle, microfine powders were developed in sunscreen products. Microfine powders have an average particle size of about 0.20 ┬Ám (micron) or less with a distribution that is narrow and well controlled. Importantly, microfine powders do not contain smaller particles; rather the lower end of the normal particle size distribution is improved through specialized manufacturing procedures. In other words, microfine powders have always been present in ZnO or TiO2 were optically overloaded by the larger particles. Therefore, microfine particles do not represent a completely new particle size, just an improvement of the existing particle size distribution.
A lot of work has been made to overcome the problems of inorganic UV filters by reducing the particle size into the nano range (