Carbon dots (CDs) are fascinating nanomaterials with technologically relevant properties; however, the effects of heteroatom doping on several properties of CDs have not been studied. In this work, a facile method for the synthesis and heteroatom doping of carbon dots from table sugar was developed using nitric acid, phosphoric acid, and sulfuric acid as simultaneous catalysts and dopants. The optical properties, phenolic content, antioxidant activity, photostability, and cytotoxicity of the CDs were measured and compared. Lascorbic acid, a well-known antioxidant, and avobenzone and oxybenzone, common UV absorbers in sunscreens, were used for comparison. Interestingly, heteroatom doping has adverse effects on several properties of the CDs as the undoped CDs yielded the highest UV-vis absorption, phenolic content, antioxidant activity, photostability, and biocompatibility. Only fluorescence quantum yields were improved by heteroatom doping. These findings will be crucial for choosing precursors for the synthesis of CDs because heteroatoms inherently present in precursors can have negative effects on the properties of the resulting CDs.