The U.S. Food and Drug Administration (FDA) requires that the presence of sulfites be declared on food labels when used as an ingredient in the food and also when used as a processing aid or when present in an ingredient used in the food (e.g. dried fruit pieces). Sulfites must be declared in these cases when the concentration in the food is ≥ 10 ppm total SO2. [21 CFR 101.100 (a)(4) "For the purposes of paragraph (a)(3) of this section, any sulfiting agent (sulfur dioxide, sodium sulfite, sodium bisulfite, potasssium bisulfite, sodium metabisulfite, and potassium metabisulfite) that has been added to any food or to any ingredient in any food and that has no technical effect in that food will be considered to be present in an insignificant amount only if no detectable amount of the agent is present in the finished food. A detectable amount of sulfiting agent is 10 parts per million or more of the sulfite in the finished food."] If naturally occurring sulfites also exists in foods, it would contribute to the analytical result. Basically, if the food contains ≥ 10 ppm total SO2, then sulfite must be declared on the label. This will most typically occur when sulfite is deliberately added to the food. The specific name of the additive (e.g. sodium bisulfite) must be declared in the case of use as an intentional ingredient.