FDA officials collected cosmetic products from various shops in Bangkok's Sam Pheng and Pahurat areas for testing and found that 57 brands - most not registered with the FDA - had prohibited substances, FDA secretary general Siriwat Thiptaradol told a press conference on Friday.

The harmful substances included hydroquinone, retinoic acid and ammoniated mercury. These could cause severe skin irritation, white spots, incurable melasma and could harm the foetus in pregnant women, Siriwat said.

Siriwat urged consumers, especially women with a melasma problem, not to buy products that did not identify their source and manufacturing date.

The list of banned cosmetics is available at www.fda.moph.go.th.

The FDA is also pushing for the punishment for manufacturers, importers and sellers of unsafe cosmetics to be increased to five years' imprisonment and a fine up to Bt500,000, he said.

The current punishment is up to one year in jail or a Bt60,000 fine.