Commerical powdered sugar often has additives like corn starch, oil, or wheat flour, so if you are allergic to any of these you could be reacting to additives.
If so make your own at home by grinding granulated sugar in a blender or coffee grinder.
powdered sugar = Puderzucker
There is no "cake powdered sugar". Powdered sugar is made from sugar, which is ground into a powdered form, with a minute amount of corn starch added to prevent it from "caking" or lumping.
potassium permanganate reacts with powdered sugar
Sugar beets can be turned into granulated sugar
Powdered sugar crystal
eHow (and confirmed by Domino) says 1c graunular sugar can be substituted for 1 3/4 c confectioner sugar, but comments say way too sweet and recommendations were made to not substitute in puddings/sauces as powdered sugar has a bit of cornstarch.
Usually one pound of powdered sugar is in a box. Which is about 2 cups.
Powdered sugar contains cornstarch which could alter the texture of the canned goods. So powdered sugar would not be a good choice when canning.
What is the shape of a round Lincoln penny? There is one cup of powdered sugar in a cup of sugar. Contrary to popular belief, this answer is wrong. Normal sugar has less efficient packing than powdered sugar, so you can fit more powdered sugar in a cup as opposed to normal sugar.
You can, it's just not marked as such. Basic powdered or confectioner's sugar unless it is marked 10x is the same as 4x powdered sugar.
Granulated sugar is just sugar. Powdered sugar has corn starch in it so that it will stay as a powder and not lump.
Flour does contain wheat, while powdered sugar and salt do not.