Sulfites are actually in darned near everything you consume, these days, but the ones that get the most attention are those found in wines. That's because a lot of folks with asthma or other problems so often claim that the sulfites in wines compound their issues, and thirty years ago the FDA classed them as an allergen.
There's just one teeny little problem, here: sulfites are a natural by-product of fermentation, and they head off bacterial proliferation that would otherwise ruin the product (and possibly sicken the drinker). So they're kind of important. As it happens, though, there's a pretty easy way to deal with them.
As an aside, reds are generally low in sulfites, while whites are often chock-full of them. It's also worth noting that there are two "flavors" of SO2 in wines: "bound" SO2 has bound to compounds in the wine, while "free" SO2 is used much more gradually as it preserves the wine.
Anyway, after all that, here's the money-shot: it turns out that a few drops of plain old hydrogen peroxide in the glass won't affect the flavor, but will neutralize virtually all of the "free" SO2, which appears to be the main allergenic culprit in the wine.