What are sulfur oxides, sulfites, and sulfates?

Sulfur oxides are molecules made of sulfur and oxygen.

SO2 = 1 sulfur and 2 oxygen.
This is called sulfur dioxide.

SO3 = 1 sulfur and 3 oxygen.
This is called sulfur trioxide.
On this same note, H2O is officially called dihydrogen oxide. However, we all call it water.

SO3, sulfur trioxide, is also called sulfite.
You can see a picture of sulfite on the right hand side of the screen, at the top.

Still with me?

SO4= 1 sulfur and 4 oxygen.
This called sulfate.

Sulfur dioxide can easily convert to sulfite in the presence of oxygen.

SO2 (g) + O2 (g) ----------- 2 SO3 (g)

But, it takes a bit more to convert sulfite to sulfate.

This is why someone sensitive to sulfites will often be sensitive to sulfur dioxide, as well-- though often will have different symptoms to each. However, someone sensitive to sulfITES is rarely sensitive to sulfATES. Is it possible? Sure. Here's one. It's just not very likely. And, thank goodness, I'm not.

This extends to medication. A medication that has a base in sulfAte is not necessarily a problem. However, if it is also sulfIted-- which most are-- then there is a big problem.

For example, codeine sulfate has a sulfate base. This is not a problem. However, almost all of the inactive ingredients are sulfited, which means that someone with a sulfite sensitivity will have a reaction, not to the codeine, but to the "inactive" ingredients.

More Information:
Wikipedia: Sulfite
Wikipedia: Sulfur Dioxide
Wikipedia: Sulfate