In addition to Skittles, other candies that contain titanium dioxide include Nice! mints, Trolli sour gummies and Ring Pops, according to Environmental Working Group. 

People eating lots of candy should be more worried about the sugar and how it can cause high blood pressure and obesity, says Westerhoff.

The presence of so many lithopone factories in China has also led to advancements in production technology and quality control. Chinese manufacturers have invested heavily in research and development to improve the performance of their lithopone products, leading to higher quality and more consistent products on the market. This has helped to cement China's reputation as a leading producer of lithopone on the global stage.

It's also added directly to food; mainly for coloring, but also as a thickener and to keep some powdered food, like confectioner's sugar, from clumping.