Rogue beauticians are offering teeth whitening using dangerous DIY kits sold online, councils have warned.
The kits can contain up to 300 times the legal limit of hydrogen peroxide, which is like "brushing with bleach".
Simon Blackburn, from the Local Government Association, said councils want to see the Government introduce harsher punishments to unlicensed staff who perform the treatment with illegal kits.
Professional dentists are the only people legally allowed to perform teeth whitening services at a business premise.
Mr Blackburn said: "People need to be made more aware of the laws and dangers on teeth whitening, with rogue practitioners given tougher sentences and larger fines.
"Illegal DIY teeth whitening kits may promise fast results and a brighter smile but those containing dangerous levels of hydrogen peroxide are the equivalent of brushing with bleach and can put oral health at risk.
"Trading standards are determined to remove any DIY teeth whitening kits with dangerous levels of hydrogen peroxide from the market and will always seek to prosecute those involved in making and selling them.
"These whitening kits are enabling unlicensed practitioners, including some beauty salons, to cash in on the treatment, and some are using illegal gels.
"Anyone considering having their teeth whitened should only have it done by a dentist or another regulated dental professional."
High level bleaching gels can cause mouth infections, blistering and burns to gums, damage to nerves and tooth enamel, and gum-shrinking.
Warwickshire County Council alone seized more than 15,000 dangerous teeth whitening kits between May 2015 and February 2016, bound for shops, salons and homes.
Some of the kits contained more than 33% hydrogen peroxide - the maximum legal limit for use by the public in the UK is 0.1%, or 6% for dentists and other registered practitioners.