People in the UK have been advised to be wary of teeth whitening kits by one expert in the field.
Martin Fallowfield from the British Dental Association told the Sun that some DIY products may not be very good for the teeth at all.
"Only dentists and dental hygienists can legally sell professional strength whitening kits in the UK," he pointed out.
Consequently, kits bought elsewhere such as on the internet or from salons can be either "useless or dangerous", Mr Freeman said.
To help get smiles looking really white, he recommended brushing twice daily and flossing as much as possible, as well as seeing a dentist if considering cosmetic dentistry treatments.
He also said it is more effective in the long run than home-based products.