E-cigarette liquid bought on Tyneside contained a potentially harmful chemical, a BBC investigation found.
Inside Out bought four liquid refills and sent them to a laboratory for testing. Three were clear but a fourth contained a chemical called diacetyl.
It is used as a flavouring in foods and experts said while it was safe to eat it was not safe to inhale and had been linked to a serious lung condition.
VIP, which distributed the refill, said it had been withdrawn from sale.
The four samples were bought in shops and markets and were sent for testing at a food control laboratory in Leeds.
The refill found to contain diacetyl was VIP's butterscotch flavour and was bought at its shop at the Metrocentre, in Gateshead.
'POPCORN WORKER'S LUNG'
Lab analyst Chris Hunt said: "It's a flavouring. It's used in foods, it's used in margarines, popcorn and a number of other food products.
"But it has this property that although it is safe to eat it is not very safe to inhale."
Dr Graham Burns, a respiratory physician at Newcastle's Royal Victoria Infirmary, said diacetyl is associated with a lung condition called popcorn worker's lung.
"It has been inhaled in significant quantities in people who worked in popcorn manufacturing factories," he said.
"In those individuals it has caused a very serious lung condition, serious enough to warrant lung transplantation."
Lynne White, VIP head of retail distribution
Lynne White, from VIP, said the firm was investigating how the chemical had got into the liquid
Lynne White, head of retail distribution at VIP, said she was "very disappointed" Inside Out had been able to buy the refill as they had detected the chemical through their own testing and it had been withdrawn about a week before it was bought.
"Because of the small amount the vaper would actually consume it was deemed in the short term there would be no health concerns", she said.
"Long-term yes there could well be, however we decided it was a withdrawal rather than a recall of the product and that was based on Ecita's (Electronic Cigarette Industry Trade Association) guidelines."
They were given spot checks and audits by Ecita, she said.
"This is our first issue in five years. We sell millions of bottles a year. We are very sorry it has happened, we are investigating how it has happened".
In July, a report in the journal Addiction suggested e-cigarettes are likely to be much less harmful than conventional cigarettes.
But, scientists are divided on the issue with some who treat smokers with a nicotine addiction seeing them as a safer alternative to cigarettes but others worry about how safe they are.
Dr Burns said: "They are as yet entirely unregulated so at the moment if you go out on to the streets, buy an e-cigarette you have no idea and I have no idea what you are putting into your lungs."
Glynis Miller suspects use of e-cigarettes were a factor in her husband's death
Ailsa Rutter, the director of Fresh North East, which was set up to tackle smoking-related death and illness in the region, said they were very open-minded about developments such as e-cigarettes.
She said: "The evidence points to the fact that these are likely to be much less harmful but we need really robust monitoring, surveillance and of course we really welcome a lot of research into these products."
Terry Miller, who was a heavy smoker from Gateshead, died of lipoid pneumonia and oil was found on his lungs nine months after he started vaping.
In 2011, a coroner recorded an open verdict at an inquest into his death, but a doctor who treated him said at the time he believed it could be associated with his use of the e-cigarettes and called for more research to be done.
Miller's widow Glynis said: "My suspicions are that it was a contributor to my husband's death."