Titanium can combine with other chemicals to make different materials. When titanium mixes with oxygen from the air, it forms titanium dioxide (TiO), or titania. Titanium dioxide is a white pigment that is often used to make things less transparent, brighter, or rougher - because it does not react with chemicals inside the human body, it is safe to use in foods and other applications, like toothpaste. Pieces of titanium metal are protected by a shell of titanium dioxide, which forms when the metal is in the air and helps prevent chemicals from damaging the metal centre. 