Aside from a minuscule amount of dye, cotton candy is pure sugar, melted and spun into a type of glass. To find out how much sugar I'd eat if I actually ate the stuff, I had to weigh it.
I weighed the candy on the paper stick, peeled it off the stick, weighed it again, and weighed the stick to double-check my math. It came out to 42.7 grams of sugar. That sounds like a lot--more than 8 Lifesavers--but on the other hand, it's about the same as a can of regular soda, and only a little more than a serving of fruit juice.
So is cotton candy the huge sugary treat it looks like? Not as much as you'd think, since most of what you see is just air). If I had split that day's cotton candy purchase among my three children, it would have been less sugar per child than giving them each a CapriSun.
Of course, how much sugar you're eating does depend on how much cotton candy you buy. My next cotton candy purchase, which had several skeins of cotton candy stuffed into a plastic bag, weighed nearly half a pound (we hurried to a nearby grocery store to find out). We only ate handfuls of that one, and experimented with the rest.