Monogamy is widely assumed to be the safer choice. A study of 10,500 Finns found that people with multiple partners had sexual health and functioning that matched or slightly beat those who were strictly monogamous.

Monogamy is usually treated as the safer, more satisfying default. A study published in the Journal of Social and Personal Relationships tested that assumption directly and found little support for it.

Researchers led by Michelle Larva-Ruhala at the University of Turku’s INVEST Research Flagship Centre ran two studies. The first surveyed 888 adults from the US, Portugal, Italy, and Finland, measuring sexual functioning, satisfaction, and STI history, and separating people into consensually non-monogamous (polyamory, open relationships) versus those keeping partners secret, meaning infidelity. The second used a population-representative Finnish sample of 10,503 people, statistically matched on age, gender, and other factors to reduce the self-selection bias that affects most non-monogamy research.

What they found

In the first study, sexual functioning was broadly similar between monogamous and non-monogamous people. Women with multiple partners reported higher desire, arousal, and satisfaction with their secondary partner than with their primary one, and higher than single-partnered women reported overall. Men’s functioning did not differ by relationship type.

Polyamorous people were 3.6 times more likely to have ever been tested for an STI, but diagnosis rates did not differ from monogamous people. Infidelity was not linked to worse sexual functioning overall; the one exception was that men who kept a secret partner reported lower satisfaction in their primary relationship.

The 10,500-person Finnish sample told a similar story. Non-monogamous men reported fewer premature ejaculation symptoms than monogamous men. Non-monogamous women reported higher sexual desire. Both sexes reported slightly higher desire toward an attractive partner. Isolating infidelity specifically, again, showed no negative effect on these outcomes.

“We were surprised by the finding that infidelity was not associated with worse outcomes,” Larva-Ruhala told PsyPost. “Both studies suggest that, on average, having multiple concurrent partners isn’t necessarily tied to poorer sexual health.”

Why the design matters

Most non-monogamy research recruits from people who already identify with the label and volunteer for surveys about it, which likely skews toward those who are doing well. The Finnish sample instead came from existing genetic and behavioral research projects not focused on non-monogamy at all, so participation wasn’t filtered by how someone felt about their relationship.

“People who are generally happy in their relationships… may be more quick to participate in these surveys,” Larva-Ruhala said. “Study 2 used data from population-representative samples in studies not focused on consensual non-monogamy, so we can assume people all across the board completed the survey, lowering some of that bias.”

What it doesn’t show

Everything here is self-reported, which can diverge from medical records, and people may recall their STI history imperfectly or answer in a favorable light. The first study’s non-monogamy category lumped together different arrangements, such as whether partners cohabited, without distinguishing them. The infidelity measure combined current and past cheating, so some participants may have reconciled long ago.

“Just because we didn’t find many differences in sexual health between those who cheat and those who practice ‘ethical’ forms of non-monogamy, doesn’t mean that doing one or the other is of no consequence,” Larva-Ruhala said. “The results certainly don’t condone infidelity. They simply show that people can maintain sexual health under both versions.”

Source

Larva MA, Rodrigues DL, Gunst A, Jern P, Nickull S, Larose MP, Rantala MJ, Mogilski JK. “Sexual Health in Monogamous and Non-Monogamous Relationships: Evidence From Convenience and Population-Based Samples.” Journal of Social and Personal Relationships, 2026.
DOI: 10.1177/02654075261475718