An unfaithful partner may harm more than your feeeeeelings, a new study reveals, after researchers looked at safety precautions taken by “cheaters” during sex versus those in negotiated non-monogamy scenarios.

Amusingly, data on cheating behaviors was culled from more than 1,600 people who responded to an online ad. (I bet they’re good at that.) Of the respondents, around 800 reported having sex with someone other than their primary partner.

What’s interesting is that negotiated non-monogamy was more common than “cheating,” or going outside an exclusive sexual relationship without the knowledge of a primary partner.

Among the 800 who reported straying from their primary relationship, 500 did so with their partner’s knowledge or consent, and 300 had sex without their primary partner’s knowledge or consent. Of the unfaithful 300, respondents were 27% less likely to use condoms during vaginal sex. When it came to even riskier anal sex, that number rose to 35% less likely.

The cheating respondents were also 64% more likely to have partaken in alcohol or drugs before getting their freak on in an unsafe and unethical way. Study author Dr. Terri Conley of the University of Michigan says open dialogue about non-monogamy and pre-negotiation can actually be protective to both partners:

“Our research suggests that people who are unfaithful to their monogamous romantic partners pose a greater risk for STIs [sexually transmitted infections] than those who actively negotiate non-monogamy in their relationship.”

Conley continues:

“Monogamy can be an effective method for preventing the spread of STIs, but only if couples test negative for STIs at the start of the relationship and remain faithful while they are together. If people do not find monogamy appealing or feasible, they clearly need to think about the risk this poses to their partner and consider whether an open relationship would suit their needs better, and better protect their relationship partners.”

The study of unsafe sex in monogamous versus non-monogamous relationships was published in the June issue of the Journal of Sexual Medicine.