One in 10 men and one in 20 women who travel internationally from Great Britain find new sexual partners abroad, according to two new studies.

Sexually transmitted infection and HIV prevalence is higher in certain parts of the world, so some overseas partnerships may be riskier than others, said the lead author of one paper.

"When people travel from home they have the opportunity to meet new people and, depending on why they are traveling, may feel less constrained by social taboos controlling sexual expression," said Dr. Clare Tanton of the Research Department of Infection and Population Health at University College London.

Tanton and colleagues analyzed responses to the British National Survey of Sexual Attitudes and Lifestyles between 2010 and 2012. Of more than 15,000 adults living in Britain who responded, over 12,000 said they had at least one sexual partner within the previous five years. About 1,000 said they had sex with a new partner while traveling overseas.

This was slightly more common for men and women under age 35, but even for those over age 35, one in 20 men and one in 40 women said they had "hooked up" abroad.

"We found that a similar proportion of people reported having had sex for the first time while overseas in our latest survey (carried out 2010-2012) as we found in the previous survey (carried out 1999-2001)," Tanton said by email.

In the more recent survey, those who had sex overseas tended to have more sexual partners total, and were less likely to use condoms in general and more likely to use drugs or alcohol than others. They were also more likely to have been to a sexual health clinic or have been tested for HIV in the past five years, according to the results in Sexually Transmitted Infections.

"Unfortunately we don't know what proportion of this sex while overseas was protected but other studies of travelers and STI clinic attendees suggest that a sizable proportion of it probably wasn't," Tanton said. "I'd like to see people think about buying and packing condoms in the same way they do for suntan lotion as part of their travel preparation."

Only one third of men and 40 percent of women who reported a partner while overseas had been to a sexual health clinic in the past five years, so improvements can still be made, she said.

One in four men who reported having a new non-UK-resident sex partner said they had paid for sex within the past five years.

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Another study in the same issue of the journal surveyed international backpackers visiting the islands of Thailand in 2013, more than half of whom were traveling without a sexual partner, and 40 percent of whom said they had sex with a new partner during the trip - often another backpacker.

Many of the travelers reported never or inconsistently using condoms, most often those from Britain or Sweden.

"The results demonstrate a mechanism by which disease may be spread from one population to another," said Christopher Lewis of the Institute of Clinical Sciences, College of Medical and Dental Sciences, at the University of Birmingham, who coauthored the second study.

"This is a particular concern as we see the emergence of antibiotic-resistant strains of gonorrhea in some parts of the world, and our worry is that gonorrhea may become an untreatable infection," he told Reuters Health by email.

Unprotected sex can lead to unplanned pregnancy, HIV infection and infertility, he said.

"Consistent condom use is the most effective means of preventing the spread of disease during intercourse," Lewis said. "We encourage all backpackers, irrespective of age and gender, to pack (and use!) condoms on their travels."

Sex may be the main purpose of travel for some people who choose to travel to Thailand, said Dr. Alberto Matteelli, of the Infectious and Tropical Diseases Clinic at the University of Brescia in Italy, who coauthored an editorial in the journal.

"There is nothing wrong with Thailand," Matteelli told Reuters Health by email. "What is wrong is the business of sex that is built at the expenses of the dignity and life of many people including a significant proportion of adolescents."