Skin-lightening creams which contain banned ingredients can pose a serious threat to consumers' health, councils have warned.
Illegal products were still available to purchase on the high street, said the Local Government Association (LGA), which represents councils in England and Wales.
The organisation has warned that the increasing popularity of skin-lightening creams had led to "inferior toxic products" infiltrating the market, containing ingredients such as bleaching agent hydroquinone and mercury.
Hydroquinone - described as the "biological equivalent of paint stripper" - can remove the top layer of skin, increasing a person's risk of skin cancer, liver and kidney damage.
Mercury can also lead to the development of life-threatening health problems.
The LGA said that "rogue retailers" who sell the illegal skin-lightening lotions frequently label the ingredients on the products incorrectly.
Skin-lightening products containing banned ingredients can also be bought at low prices online, at car boot sales and from market stalls.
"Skin creams containing banned ingredients are very dangerous and could seriously damage your health, scar you for life and even kill you, so they should be avoided at all costs," said Simon Blackburn, chair of the LGA's Safer and Stronger Communities Board.
"Consumers should always check the ingredients of their skin creams, be suspicious of very low prices which are likely to indicate the lotion is fake and potentially harmful, and never use a product containing hydroquinone. If the product doesn't display the ingredients at all, then don't use it."
Skin-lightening products are typically targeted at consumers who are black or from ethnic minorities.
The creams can also be used to lighten hyperpigmentation and treat acne scarring.
Those which are purchased on prescription should only be used under the supervision of a doctor, the LGA advised.
The cost of buying skin-lightening products which do not contain banned ingredients can be high, which is why "toxic" alternatives are being sold at a cheaper price.
"Councils have been targeting rogue retailers selling these banned creams and people should report any concerns so that town halls can take action to prevent anyone from buying these lotions, potentially ruining their looks forever," Mr Blackburn said.
If retailers are found selling illegal skin-lightening creams, they could face fines of up to £20,000 and prosecution.
Mr Blackburn added that next year's governmental Spending Review "needs to provide the long-term, sustainable settlement councils need to ensure trading standards teams are sufficiently funded to protect the public from harm".
In 2017, the global skin-lightening industry was valued at an estimated $4.8bn (£3.9bn), the LGA said.
By 2027, it is predicted to grow to a worth of $8.9bn (£7.3bn).
Illegal skin-lightening creams can be imported to the UK from other areas of the world including Pakistan, the Middle East and the Caribbean.
Southwark Council recently seized 275 products from a cosmetics store after an investigation found some of the items contained hydroquinone.
Meanwhile, 360 skin-lightening products were recently seized from a store in Dagenham, some of which contained the harmful bleaching agent.
The LGA said that if anyone is suspicious of a cream they have purchased, they should stop using it straight away.