RESORCINOL COMPOSITION

1. A topical pharmaceutical composition for lightening skin or reducing the pigmentation of skin in a human, comprising an amount of a compound of formula I or a pharmaceutically acceptable salt thereof, which amount is effective in lightening skin or reducing the pigmentation of skin, and a pharmaceutically acceptable carrier. 2. The composition of claim 1, further comprising a sunscreen. 3. The composition of claim 1, further comprising resveratrol or another active agent that is an anti-oxidant. 4. The composition of claim 1, further comprising retinoic acid or a derivative of retinoic acid. 5. The composition of claim 1, further comprising glycolic acid, trichloroacetic acid or another skin peeling agent. 6. The composition of claim 1, which is in the form of a water-alcohol solution, an oil-in-water emulsion, a water-in-oil emulsion, an emulsified gel, or a two-phase system. 7. The composition of claim 1, which is in the form of a lotion, cream, milk, gel, jelly, paste, ointment, salve, mask, microspheres, nanospheres, or a vesicular dispersion. 8. A method of lightening skin or reducing the pigmentation of skin in a human, comprising administering to said human an amount of a compound of formula I or a pharmaceutically acceptable salt thereof, which amount is effective in lightening skin or reducing the pigmentation of skin. 9. The method of claim 8, in which the compound of formula I or the pharmaceutically acceptable salt thereof is formulated in a water-alcohol solution, an oil-in-water emulsion, a water-in-oil emulsion, an emulsified gel, or a two-phase system. 10. The method of claim 8, in which the compound of formula I or the pharmaceutically acceptable salt thereof is formulated in a lotion, cream, milk, gel, jelly, paste, ointment, salve, mask, microspheres, nanospheres, or a vesicular dispersion. 11. A topical pharmaceutical composition for inhibiting tyrosinase in a human, comprising a tyrosinase-inhibiting effective amount of a compound of formula I or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier. 12. The composition of claim 11, which is in the form of a water-alcohol solution, an oil-in-water emulsion, a water-in-oil emulsion, an emulsified gel, or a two-phase system. 13. The composition of claim 11, which is in the form of a lotion, cream, milk, gel, jelly, paste, ointment, salve, mask, microspheres, nanospheres, or a vesicular dispersion. 14. A method of inhibiting tyrosinase in a human, compri