Researchers found many adults acquire new sexual partners when abroad, but they may be putting their health at risk by doing so.
The studies found that these adults are less likely to engage in safe sex practices - such as condom use - and more likely to engage in other risky behaviors, including use of alcohol and illicit drugs.
The two papers were recently published in Sexually Transmitted Infections - a journal of The BMJ.
For the first study, co-author Dr. Clare Tanton, of the Research Department of Infection & Population Health at University College London, United Kingdom, and colleagues analyzed data from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3).
The researchers identified 12,530 people aged 16-74 who reported having at least one sexual partner in the previous 5 years.
Of these individuals, around 1 in 10 men and 1 in 20 women reported having had sex with a new partner during their travels abroad in the past 5 years.
On assessing results by age, the researchers found that 1 in 20 men and 1 in 40 women aged 35 and older reported having had sex with a new partner while abroad.
According to the team, these numbers are likely to rise alongside the aging population and the increase in relationship breakdowns.
"These proportions are likely to increase as older people maintain good health, have the financial means to travel, and are now more likely to experience partnership breakdown," they explain, "and so older age groups should also be considered for health promotion messages by health professionals when consulting for travel advice."
Risky behavior higher for travelers who have sex with new partners
Adults who reported having sex with a new partner on their travels were more likely to have a higher number of sexual partners overall, the researchers report, and they were also more likely to have engaged in risky behaviors, such as having sex without a condom, using illicit drugs and excess alcohol use.
Visits to a sexual health clinic were more common among adults who had sex with new partners while abroad, as were reports of being tested for HIV or receiving a diagnosis of a sexually transmitted infection (STI).
Men were more likely to have had sex with at least one new partner that was not from the U.K. during overseas travels than women, the researchers found, at 72 percent and 58 percent, respectively.
Individuals in this group reported a higher number of sexual partners, and they were also more likely to have had more than one sexual partner at the same time.
Men in this group were also more likely to have paid for sex, with 1 in 4 men reporting having ever paid for sex with a partner from outside the U.K. or having done so in the past 5 years.
This behavior was more common in older men aged 35-74 than younger men, according to the team, and these men also had more sexual partners than younger men.
Overall, the authors say their findings indicate that those who engage in sex with new partners while overseas are more likely to engage in behaviors that may negatively impact their health.
"Sex while overseas may itself be less likely to be protected with the 'freedom' of travel, and also potentially in the context of other behaviors like alcohol and drug use, which may prevent people from adopting safer-sex behaviors, putting them at risk of transmitting and acquiring STIs, as well as other adverse sexual health outcomes including unintended pregnancy and sexual violence.
This argues for the importance of holistic travel advice addressing sex in the context of broader health behaviors."
Many backpackers having unprotected sex
In the second study, C T. Lewis, of the Institute of Clinical Sciences at the University of Birmingham, U.K., and colleagues set out to identify the proportion of backpackers in Thailand who engage in unsafe sex.
The team analyzed data from a questionnaire completed by 2,013 backpackers - most of whom were aged 25 and under - who visited the Thai islands Koh Phangan and Koh Tao in 2013.
Participants were asked about their sexual engagement and practices during their trip.
Around 61.5 percent of the respondents said they were traveling without a long-term sexual partner, of whom around 39.1 percent reported having sex with a new partner.
Almost 37 percent of these participants reported no or erratic condom use, according to the team, and more than a third of those who said they had packed condoms failed to use them.
The researchers note that inconsistent condom use was highest among British and Swedish backpackers, which correlates with higher rates of STIs in those nationalities.
German backpackers were less likely to have had unprotected sex than British backpackers, though they were also less likely to have had new sexual partners during their travels.
The authors note that their study only included backpackers traveling in Thailand, so whether the results apply to all young travelers is unclear.
However, they believe their findings suggest that young travelers may benefit from information on safe sex during their time abroad, adding:
"In an era of growing antibiotic resistance and continuing HIV transmission, targeting unsafe sex in backpackers has the potential to reduce STI incidence internationally."
In an editorial accompanying both studies, Drs. Alberto Matteelli and Susanna Capone, of the Infectious and Tropical Diseases Clinic at the University of Brescia, Italy, say the results may have important implications, given the significant rise in international travel in recent decades.
"The consequences on STIs could be substantial. STIs have uneven geographical distribution, and travelers may act as bridges between high-burden and low-burden countries," they note.
They add that, at present, there are no patented interventions that can encourage safer sex practices among travelers, but they say this is something that needs to be investigated in future research.