Scientists from a group of American universities, including Yale, Johns Hopkins and Princeton have found exposure to e-cigarette vapour creates a "tumour-promoting environment" in the breast and elsewhere in the body. A surgeon at the London Breast Institute at the Princess Grace Hospital named Professor Kefah Mokbel warned the findings should be a wake-up call to those who think the devices are harmless, or better than smoking normal cigarettes.

"This study provides a good level of evidence that vaping has the potential to induce breast cancer and promote its progression and spread to the lungs," he said.