Spotlight uses the active ingredient hydrogen peroxide which is clinically proven to whiten teeth. Spotlight is also clinically proven. In saying this there are many factors that may contribute to the rate of whitening to your teeth. 1. If you consume large amounts of tea & coffee before or during your whitening process this will affect the whitening rate, as they contain tannins that stain your teeth. 2. Avoid dark coloured foods such as curries, anything tomato-based and chocolate as these also promote staining to occur. We normally recommend avoiding dark coloured foods and liquids, especially during the 2-week whitening course. 3. Smoking - smoking contributes to staining of the teeth as nicotine, tar and other chemicals stain the teeth. 4. Condition of enamel - if you have damage to your enamel, over time, dentine becomes exposed - which is yellow in colour. 5. If you haven't visited your dentist in 6 months, you may have a build up of plaque and tartar that stops the active ingredients in the strips from penetrating onto the enamel which will result in a less that ideal whitening treatment. Please ensure to see your dentist and hygienist regularly. Depending on the results a person wants to achieve, they may require a second box. I hope this information helps.