Cosmetics which claim to lighten skin by using cancer-linked chemical hydroquinone were banned in the EU in 2001.
A BBC reporter was able to buy six creams and three tested positive for hydroquinone.
Analytical chemist Andrew Reid said of the chemical: "It kills cells. It's the sort of thing used to clean toilets."
Reaction to skin bleaching investigation, plus more Coventry news
The undercover BBC Coventry & Warwickshire reporter visited 13 shops that predominantly serve people from Afro-Caribbean and Asian communities in and around Coventry.
They bought six illegal skin bleaching products from six of the shops.
Mr Reid, head of life sciences at Coventry University, said: "Three out of the six products we tested did indeed contain the nasty chemical hydroquinone.
"That's a dangerous substance which will destroy the melanin producing cells.
"The sun will damage your skin and you could end up with a cancers like melanoma or leukaemia."
Aspiring model Mutsa Chikwana, 24, of Holbrooks, Coventry, said she started using a skin lightening product after a photographer edited pictures to show her skin a few shades lighter.
"He said [the photographs] had to be a certain shade," said Ms Chikwana.
"It's quite shocking. It did not look like me.
"But if you look at the pageants it's always the light skinned girl that's won, or it's always the light skinned girl that's got that top job."
A social media campaign - #unfairandlovely - is working to challenge the widely-held belief in many parts of the world that fair skin is the most attractive.
Prof Steve Garner, head of criminology and sociology at Birmingham City University, is studying the use of skin lightening products in England.
A study in Birmingham, Bristol and London found the majority of Black or Asian woman using the creams were aged 16-24.
He said: "This problem is going to get exponentially worse unless we deal with it... and that's in terms of public health and regulating the laws that do exist.
"The ideas around using skin lighteners to change your appearance are, in some cases, borderline mental health issues."
National Trading Standards has joined with UK Border Force officials to tackle banned skin lightening products getting into the country.
Warwickshire Trading Standards officer Eleanor Lake said the authority had seized 1,000 illegal skin lightening products at Coventry airport since May.
"We've found that some of them have contained up to 13% hydroquinone and significant amounts of mercury and these are dangerous substances which can lead to cancers," said Ms Lake.
"The idea is that they're putting these products on their skin to make themselves more beautiful  - but ultimately they're causing themselves harm."
Illegal skin bleaching products are being sold in shops in Coventry, a BBC investigation has found.