Almost half of men who pay for sex already have a partner, according to a report.
A study by NHS Greater Glasgow and Clyde also revealed that men "playing away" on holiday are twice as likely to have unprotected sex as those paying for sex at home.
The research, which appears in October's Sexually Transmitted Infections Journal, surveyed more than 2,600 men attending the Sandyford sexual health clinic in Glasgow between October 2002 and February 2004.
A standard health screening questionnaire completed by the men revealed that one in 10 had paid for sex. Almost half, 43%, said they were in another relationship when they had paid for the sex, and 56% of those who said they had paid for unprotected intercourse already had a partner at the time.
More than half the men asked said they had paid for sex while abroad, four out of 10 said they had paid for sex locally, and around 2% said they had paid for sex both in the UK and abroad.
Around a quarter said they repeatedly used prostitutes, with unprotected sex almost twice as common among those who paid for sex while abroad.
Although none of the men surveyed had HIV or Aids, a fifth had a sexually transmitted infection, including gonorrhoea, chlamydia and syphilis. Another finding of the study was that there was a high volume of men paying for unprotected oral sex locally and that half of these men were in long-term relationships.
Dr Tamsin Groom, who co-authored the study with Dr Rak Nandwani, said: "Very little is really known about these men, their behaviours and the risks they may pose to themselves or indeed their partners.
"Exploring the issue of paid-for sex allows us to target health promotion and services to people engaged in prostitution, their clients and the partners of both of those groups. It may in future be useful to point out these risks to the men who pay for sex so they can protect themselves as well as those they care about."
NHS Greater Glasgow and Clyde's head of inequalities and health improvement, Sue Laughlin, said: "NHS Greater Glasgow and Clyde, alongside its partners, has made a commitment to addressing the issue of prostitution.
