Hong Kong has a large sex industry - exactly how big is uncertain because the government refuses to officially acknowledge its existence. The shades of legal grey mean that prostitutes, of whom there are tens to hundreds of thousands, work in a dangerous environment. Two just-concluded trials vividly showed this, with two men sentenced to life in prison for gruesome killings. The situation is unacceptable. In the case that ended yesterday, the three victims worked in so-called one-woman brothels, the only legal form of prostitution in our city. Anyone living off the proceeds of prostitution - security guards, for example - is breaking the law. The circumstances ideally suited Nadeem Razaq, who killed the women and stole their belongings. Ting Kai-tai was jailed on Monday for the brutal murder of a 16-year-old girl involved in what is known as compensated dating. The term is misleading: any sex act which involves pre-arranged payment of cash or gifts is prostitution. Teenagers caught up in our consumer culture are increasingly turning to sex for money to fund their lifestyles. They must be discouraged from doing so. Sex can also be bought in nightclubs, discos, karaoke lounges, saunas, massage parlours, hotels and from websites and street-walkers. Prostitutes have limited means of protecting themselves. The industry is too complex for police raids to make much of a dent. Legalising prostitution is, for now, not an option. It is unlikely there would be sufficient support in society for such a radical move. Nor can we outlaw it: doing so would only drive it further underground. But the trials indicate a need for prompt change. Measures that could be adopted include allowing two-woman brothels, or permitting prostitutes to hire security guards. This would make them less vulnerable. Funding sex worker support groups to improve education and improving relations between prostitutes and police would also help. Prostitution is not going to disappear. More effort has to be made to warn of the dangers of the industry. Concerted steps have to be taken to improve the safety of those involved.