A topical composition for reducing pigmentation in human skin, comprising: (i) an effective amount of a tyrosinase inhibitor comprising 3,3'-thiodipropionic acid, or a salt or ester thereof, and (ii) an effective amount of a melanosome-transfer inhibitor comprising nicotinamide, or salt thereof, or a compound structure of formula II: wherein "n" is an integer 0 or 1; Z is selected from the group consisting of O, S, NH, and NR N; G and Q are independently selected from the group consisting of hydrogen, R N, -COR, - CO 2 R, -C(=O)NHR, - C(=O)NR 2, -PO 3 R, -S m R, -NHR, -N=CHR, -NR(C=O)R; and -NRCO 2 R; where " m " is 0, 1, or 2; and wherein G and Q may together form a 3-6 membered heterocyclic ring; and where Z and G may together form a 5 or 6-member heterocylic ring; X and Y are independently selected from groups R; and where X and Y may together to form 4-6 membered ring; R is independently at each occurrence selected from hydrogen, -F; -Cl; -Br; -I; -OH, -OR*; -NH 2; -NHR*; -N(R*) 2; -N(R*) 3 +; -N(R*)-OH; -N(→O)(R*) 2; -O-N(R*) 2; -N(R*)-O-R*; -N(R*)-N(R*) 2; -C=N-R*; -N=C(R*) 2; -C=N-N(R*) 2; -C(=NR*)-N(R*) 2; - SH; -SR*; -CN; -NC; -(C=O)-R*; -CHO; -CO 2 H; -CO 2 -; -CO 2 R*; -(C=O)-S-R*; - O-(C=O)-H; -O-(C=O)-R*; -S-(C=O)-R*; -(C=O)-NH 2; -(C=O)-N(R*) 2; -(C=O)-NHNH 2; -O-(C=O)-NHNH 2; -(C=S)-NH 2; -(C=S)-N(R*) 2; -N(R*)-CHO; -N(R*)-(C=O)-R*; -(C=NR)-O-R*; -O-(C=NR*)-R*, -SCN; -NCS; -NSO; -SSR*; -N(R*)-C(=O)-N(R*) 2; -N(R*)-C(=S)-N(R*) 2; -SO 2 -R*; -O-S(=O) 2 -R*; -S(=O) 2 -OR*; - N(R*)-SO 2 -R*; -SO 2 -N(R*) 2; -O-SO 3 -; -O-S(=O) 2 -OR*; -O-S(=O)-OR*; -O-S(=O)-R*; -S(=O)-OR*; -S(=O)-R*; -NO; -NO 2; -NO 3; -O-NO; -O-NO 2; -N 3; -N 2 -R*; -N(C 2 H 4); -Si(R*) 3; -CF 3; -O-CF 3; -PR* 2; -O-P(=O)(OR*) 2; -P(=O)(OR*) 2; perfluoroalkyl; an aliphatic C 1 -C 12 hydrocarbon radical; a C 6 -C 12 aromatic hydrocarbon radical; and a C 3 -C 12 heteroaryl radical; R N and R* are selected independently from hydrogen or a saturated, partially saturated, or aromatic C 1 -C 20 hydrocarbon radical, optionally substituted with a group R or with 1-6 heteroatoms selected from nitrogen, oxygen, sulfur, or halogen or salt thereof, and (iii) a cosmetically or dermatologically acceptable vehicle. wherein "n" is an integer 0 or 1; Z is selected from the group consisting of O, S, NH, and NR N; G and Q are independently selected from the group consisting of hydrogen, R N, -COR, - CO 2 R, -C(=O)NHR, - C(=O)NR 2, -PO 3 R, -S m R, -NHR, -N=CHR, -NR(C=O)R; and -NRCO 2 R; where " m " is 0, 1, or 2; and wherein G and Q may together form a 3-6 membered heterocyclic ring; and where Z and G may together form a 5 or 6-member heterocylic ring; X and Y are independently selected from groups R; and where X and Y may together to form 4-6 membered ring; R is independently at each occurrence selected from hydrogen, -F; -Cl; -Br; -I; -OH, -OR*; -NH 2; -NHR*; -N(R*) 2; -N(R*) 3 +; -N(R*)-OH; -N(→O)(R*) 2; -O-N(R*) 2; -N(R*)-O-R*; -N(R*)-N(R*) 2; -C=N-R*; -N=C(R*) 2; -C=N-N(R*) 2; -C(=NR*)-N(R*) 2; - SH; -SR*; -CN; -NC; -(C=O)-R*; -CHO; -CO 2 H; -CO 2 -; -CO 2 R*; -(C=O)-S-R*; - O-(C=O)-H; -O-(C=O)-R*; -S-(C=O)-R*; -(C=O)-NH 2; -(C=O)-N(R*) 2; -(C=O)-NHNH 2; -O-(C=O)-NHNH 2; -(C=S)-NH 2; -(C=S)-N(R*) 2; -N(R*)-CHO; -N(R*)-(C=O)-R*; -(C=NR)-O-R*; -O-(C=NR*)-R*, -SCN; -NCS; -NSO; -SSR*; -N(R*)-C(=O)-N(R*) 2; -N(R*)-C(=S)-N(R*) 2; -SO 2 -R*; -O-S(=O) 2 -R*; -S(=O) 2 -OR*; - N(R*)-SO 2 -R*; -SO 2 -N(R*) 2; -O-SO 3 -; -O-S(=O) 2 -OR*; -O-S(=O)-OR*; -O-S(=O)-R*; -S(=O)-OR*; -S(=O)-R*; -NO; -NO 2; -NO 3; -O-NO; -O-NO 2; -N 3; -N 2 -R*; -N(C 2 H 4); -Si(R*) 3; -CF 3; -O-CF 3; -PR* 2; -O-P(=O)(OR*) 2; -P(=O)(OR*) 2; perfluoroalkyl; an aliphatic C 1 -C 12 hydrocarbon radical; a C 6 -C 12 aromatic hydrocarbon radical; and a C 3 -C 12 heteroaryl radical; R N and R* are selected independently from hydrogen or a saturated, partially saturated, or aromatic C 1 -C 20 hydrocarbon radical, optionally substituted with a group R or with 1-6 heteroatoms selected from nitrogen, oxygen, sulfur, or halogen or salt thereof, and (iii) a cosmetically or dermatologically acceptable vehicle.