CSPI’s Chemical Cuisine is the web’s definitive rating of the chemicals used to preserve foods and affect their taste, texture, or appearance. Besides titanium dioxide, the group recommends avoiding artificial sweeteners like aspartame, acesulfame potassium, and sucralose, as well as synthetic food dyes like Yellow 5 and Red 3. CSPI and others have recently asked the Food and Drug Administration to ban the latter dye in foods and ingested drugs because the FDA has already determined that it is a carcinogen unsafe for use in cosmetics.

Mars Wrigley, the company that makes Skittles, is being sued by a California man who claims the candy contains a known toxin that poses such a serious health risk that Skittles are unfit for human consumption.

Titanium dioxide, or TiO2, sometimes referred to as E171, is an inorganic, solid substance used in a wide range of consumer goods including cosmetics, paint, plastic and food, according to the American Chemistry Council.

In food, titanium dioxide is often used as an artificial color additive. Tasha Stoiber, senior scientist at the consumer health nonprofit Environmental Working Group, says titanium dioxide can generally be thought of as a paint primer – it often goes on a hard-shelled candy like Skittles before the color is added to give it a uniform shine.