Physical sunscreens are particles that scatter and reflect UV energy back into the environment. In sufficient quantities, they will serve as a physical barrier to incident UV and visible light. Their popularity has grown in recent years due primarily to their low toxicity profile. These agents are fairly photostable and have not been shown to induce phototoxic or photoallergic reactions. They are also extremely effective in protecting against both UVA and UVB. The most common particulate sunscreen agents are titanium dioxide and zinc oxide.
Early formulations of physical sunscreen agents were not widely accepted because the particulate matters had to be incorporated in high concentrations, resulting in an opaque film on the skin in order to achieve adequate protection. This was often not cosmetically acceptable. Newer formulations which provide “micronized” formulations give rise to a more translucent appearance, and allow for adequate protection with improved cosmetic results. Comparison between zinc oxide and titanium dioxide showed that zinc oxide is superior for UVA protection in the 340-380 nm range and tends to be less pasty on the skin (45).