 It is widely accepted that current tooth whitening treatment effect is based on the oxidizing action of peroxides, even if the mechanism of action remains still unclear. Treatments are claimed to be safe, but several secondary effects have been described, since long application times and high concentrations are needed. A faster whitening ingredient which permits the use of lower concentrations and shorter application times could potentially overcome this problem. In this work, a different approach based on a reducing agent, sodium metabisulfite (MBS), is explored.