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Recent studies have shown that nicotinamide adenine dinucleotide ��NAD�� is not only a co-enzyme in cellular oxidation-reduction reactions, but also a substrate for reactions catalyzed by mono ��ADP-ribose�� transferases, poly ��ADP-ribose�� polymerases and acetylase, and it play important roles in numerous cellular physiologic functions. Nicotinamide is not only a precursor for the synthesis of NAD, but also an inhibitor of NAD-consuming enzymes. Besides pellagra, nicotinamide has been used to treat immune bullous diseases, atopic dermatitis, rosacea and acne, and so on. Moreover, nicotinamide has shown a favorable perspective in anti-skin aging and cosmetic dermatology. The safety of topical nicotinamide has been already confirmed, but a formal safety evaluation routinely designed for a new drug has not been performed for oral nicotinamide at high dose.