Despite Department of Health approval, some still doubt the treatment's safety Overuse of the popular cosmetic treatment Botox may cause muscle damage that leaves the face expressionless, doctors warned yesterday. The warning came after the Department of Health approved the use of botulinum toxin type A - a strong poison produced by the bacterium Clostridium botulinum - as an anti-wrinkle treatment last month. Botox is a brand of the toxin manufactured by Allergan, a pharmaceutical company based in the United States. General medical practitioner Wu Tien-tze explained that Botox worked by paralysing the muscles of the face. 'When these muscles relax, the fine lines and wrinkles smooth out,' he said. The treatment 'seems' safe for the time being, but cases of permanent damage had been seen and it was probably too early to say for sure, he said. An article in April last year in the Los Angeles Times, citing a University of California dermatology professor, said: 'Overuse of Botox injections can result in the loss of facial expression. Even worse, an injection into the wrong muscles can cause droopy eyelids, asymmetric smiles or even drooling'. However, Allergan says on its website the product has 'been proven as a safe and effective therapy, and has been widely used for more than 11 years'. Cases of muscle damage had been known to have been caused by Botox, said plastic surgery specialist Francis Ho at a press conference hosted by Allergan yesterday. In small quantities, however, Botox could improve all types of wrinkles from brow furrows and crow's feet to frown lines on the forehead, said Dr Ho, who owns a private cosmetic surgery clinic. Side effects were minor, with the most common ones being short-lived headaches and nausea, he said, adding it was important to go to a qualified practitioner and not just any beauty parlour. The use of Botox to smooth out wrinkles was approved by the Department of Health last month but the substance had been used for the treatment of muscle disorders such as lazy eyes, tics and uncontrolled blinking by medical practitioners since 1994, Dr Ho said. The Department of Health yesterday did not comment on how Botox would be regulated. A Ms Leung, 47, speaking at the press conference, said each treatment lasted about 10 minutes and cost about $3,000 to $4,000. She had her first Botox treatment about 18 months ago. 'It's about having the choice to look better, just like wearing clothes,' she said. Dr Wu said: 'Think carefully before opting for these treatments ... there is no return once you start because you get used to looking younger than you are.'