Teeth whitening treatments are not recommended for users under 18 years of age, or women who are pregnant or breastfeeding. Whitening kits will also not work on crowns, veneers or false teeth, so if you have any of these speak to your dentist. Don’t use the strips immediately after dental treatments such as crowns or fillings, or if you wear orthodontic braces.
Be cautious buying stronger products that are not licenced for use in the UK (Crest Whitestrips are a popular example sold over the counter in the US but not in the UK). Websites claiming to sell these and similar products in the UK are not acting legally, and may well be selling counterfeit versions.