Titanium is one of the most common metals on earth, but it does not occur naturally in this elemental form. TiO2, also known as titanium (IV) oxide or titania, is the naturally occurring compound created when titanium reacts with the oxygen in the air. As an oxide, titanium is found in minerals in the earth’s crust. It is also found with other elements, including calcium and iron.
There is also some evidence to suggest that exposure to titanium dioxide nanoparticles may be harmful or toxic to the environment, including aquatic life and other organisms. The production and disposal of the mineral may also release pollutants, such as carbon dioxide and sulfur dioxide, into the air and water.

Recent analyses of food-grade TiO2 samples have found that a significant portion of particles may be within the nanoscale. These particles (also known as nanoparticles) range in size from 1 to 100 nm, where 1 nm equals 1 billionth of a metre (the width of a typical human hair is 80,000 to 100,000 nm).
4. Water-Resistant Titanium dioxide-based sunscreens tend to be more water-resistant than those containing chemical sunscreen ingredients, making them a good choice for outdoor activities.