One dermatologist warned that if doctors misled patients into believing the treatment worked they could face disciplinary action.

They were commenting after a South China Morning Post reporter, posing as a customer, called a group of beauty salons and visited a skin clinic and was offered a series of treatment sessions at prices ranging from HK$680 to HK$1,500 a time.

A doctor at a Central clinic admitted there was no scientific evidence that the treatment would whiten skin but it had been used in the region for 30 years and there was no harm in trying it.

At one of the salons, a staff member said the procedure - in which various ingredients in a saline solution are introduced directly into patients' veins - was 'a hit' among celebrities in Taiwan.

Patients are put on the drips for 15 to 30 minutes once a week for a course of 10 sessions.

Dermatologist Henry Chan Hin-lee said he doubted the efficacy and safety of the treatment.

'There is no evidence base to prove that injecting these ingredients into someone's vein can make their skin whiter,' he said. 'People can get infections if the production process is not strict enough and the solution gets contaminated.'

Dermatologist Louis Shih Tai-cho said common proven medical methods for skin whitening included pills, lasers and intense pulsed light treatments, but not vein injections.

He warned that doctors who misled people into believing the treatments worked could face disciplinary action by the Medical Council and even be struck from the register.

A staff member at the salon group said clients were put on a saline drip mixed with ingredients such as the antioxidants vitamin C and glutathione, and a non-steroidal anti-inflammatory drug, tranexamic acid.

She said the drip would last for 15 to 30 minutes and a treatment usually consisted of 10 drips in total, with drips once or twice a week.

People who were pregnant, sick or menstruating should not have the treatment, she said.

'You don't need to be worried,' she said, adding that a registered doctor would be in charge. 'It is very safe. Many people receive the treatment. Many Taiwan celebrities undergo the treatment.'

At the Central clinic, the reporter was told the method had been used in Japan and Korea for more than 30 years for skin care.

'Based on the composition of the ingredients, although there are no scientific journals supporting its whitening function, we believe there is no harm in trying an alternative method,' the doctor, who qualified in Britain, said.

He said the solutions he used were registered with the Department of Health and were imported from Japan. He said the treatment had few side effects, but some people might suffer from dizziness and insomnia.

The Department of Health said vitamin C and tranexamic acid were pharmaceutical products under the Pharmacy and Poisons Ordinance and must be registered with the Pharmacy and Poisons Board before being put on sale.

A spokesman said there was no scientific evidence to show that injecting vitamin C and tranexamic acid could have a whitening effect on the skin. But doctors could still offer the treatment as a complementary or alternative method. 'Clients should protect their interests and rights by ensuring that their choices are informed ones,' the spokesman said.