Electronic cigarettes were found to contain one million times more cancer-causing substances than outdoor air in a study by Baptist University.
Researchers also discovered a type of flame retardant that affected the reproductive system and could lead to cancer.
The Hong Kong Council on Smoking and Health called for a ban on e-cigarettes .
In analysing 13 types of e-cigarettes bought on the market, researchers found that the level of polycyclic aromatic hydrocarbons (PAHs) – a by-product of burning petroleum that is commonly detected in roadside air – ranged from 2.9 to 504.5 nanograms per millilitre.
The substance, which contains highly carcinogenic chemicals such as benzo(a)pryene, also carries various chemicals that promote growth of cancer cells.
“[Level of PAHs] in e-cigarettes is at least one million times more than roadside air in Hong Kong,” said Dr Chung Shan-shan, assistant professor in the university’s biology department.
Polybrominated diphenyl ethers (PBDEs), a flame retardant used mainly in furniture and electronic products, were detected in a range of 1.7 to 1,490ng/ml in the 13 brands of e-cigarettes.
That level was much higher than in two samples of conventional cigarettes used in the study.
The Food and Health Bureau said it was discussing laws to ban e-cigarettes and hoped to submit a proposal to the Legislative Council as soon as possible.