Sulphur

Sugar processors add lime to the cane juice to coagulate the impurities. The juice is then neutralised with sulphur dioxide to settle out impurities. Sugar producers also add sodium hydrogen sulphate at the final stages of boiling. This releases sulphur dioxide into the juice and lightens the color of the final product. (Note: A high sulphur content often remains in the final product.)

People who are sensitive to sulfur may have an allergic reaction to the "pure white sugar". - 609