Sulfites are found in wine grapes, and occur naturally in almost all wines. But the debate over sulfite use continues in the wine-making community.
Sulfites (sometimes spelled "sulphites") in the form of sulfur dioxide are sometimes added to wines to stabilize and preserve the wine. The health effects of sulfites are debatable, but some people claim to have a sulfite allergy and react to these compounds with a headache or other allergic response.
In order to be labeled as "USDA Organic," no sulfites can be added to the wine. If sulfites are added, the wine can be labeled as "Made With Organic Grapes," but it falls short of full USDA Organic certification.
Biodynamic wines, so-called "natural wines," vegan wines and other types of wines may or may not have added sulfites -- it's also important to remember that labeling requirements vary from country to country, so in all cases, check the label to see if the wine contains sulfites.