In legal speak, a crime of passion is one that occurs without premeditation. You didn’t plan on strangling your neighbor’s pet ferret, but the thing was crying out all night and your impulses got the better of you. New research suggests the same phenomenon occurs when we feel such intense empathy for someone that we are willing to hurt others.

A study conducted by University of Buffalo researchers finds our feelings of love can compel us to do harmful and sometimes violent things to other people, even when they haven’t afflicted us personally. We have two neurohormones to thank — oxytocin and vasopressin — which act as both hormones in our blood and neurotransmitters in our brain. They affect our behavior and regulate our mood in a one-two punch of love and aggression.

“Both oxytocin and vasopressin seem to serve a function leading to increased ‘approach behaviors,’” said Michael J. Poulin, associate professor of psychology at UB, in a statement. Approach behaviors are the movements me make toward other people or objects. Though, unlike avoidant behaviors, which tend to stem from negative reactions, approach behaviors can arise from either feelings of closeness or aggression.

Hoping to learn more, the two researchers conducted a survey and an experiment. The survey asked people about a loved one that had recently felt threatened by a third party, to which people described their emotional reactions to that threat. The responses were generally negative in nature, which “wasn’t surprising,” Poulin said.

But the follow-up experiment offered some interesting results. First, Poulin and Buffone collected saliva samples to measure neurohormone levels. They then told the subjects a story meant to evoke compassion. The subjects learned about two fictional characters who were in a separate room together and about to take a math test. One character was portrayed in a positive light, while the other was given a more sour reputation. They were part of a study designed to see how hot sauce, a painful yet harmless stimulus, would affect test-taking ability. Having learned all this, the real subjects were given the power to choose how much hot sauce the third-party character would be exposed to.

So how did they decide the third party’s fate? Just as a mama bear would if her cub were in danger. “The results of both the survey and the experiment indicate that the feelings we have when other people are in need, what we broadly call empathic concern or compassion, can predict aggression on behalf of those in need,” Poulin said.

The findings reinforce what zoologists have observed in nature and what anthropologists have found in society. A raging sense of empathy can cause attacks on those near to us to feel like attacks on us. Oxytocin, the love hormone, and one we get a surge of when we hug or kiss someone, floods our body. Meanwhile, traces of vasopressin get released straight to the brain, promoting social behavior and a response to stress.

So we swoop in, looking to put out the fire as if our very lives, or test-taking abilities, were at stake. But that’s not the end of it. Poulin suspects we also manifest this behavior even when no harm is present. The fictional villain wasn’t doing anything particularly villainous; he just happened to be taking the same test as our fictional buddy. Still, we react all the same.

“In situations where we care about someone very much, as humans, we were motivated to benefit them,” Poulin said. “But if there is someone else in the way, we may do things to harm that third party.” We won’t necessarily be exempt from punishment — crimes of passion are still crimes — but at least science can explain why we get locked up.

Source: Buffone A, Poulin M. Empathy, Target Distress, and Neurohormone Genes Interact to Predict Aggression for Others–Even Without Provocation. Personality and Social Psychology Bulletin. 2014.