“Stand up straight and look people in the eye”—so go the most basic commandments of engaging confidently with your fellow humans. But a new study finds that eye contact is not a blanket solution to persuading your conversation partners. Depending on how someone’s opinions square up to yours, eye contact can have the opposite effect.

Prior research and anecdotal evidence suggest that people who make eye contact are more “persuasive, likable, and competent,” write the study’s authors. But regardless of how persuasive a person may seem because they look others in the eye, if their message is somehow controversial or disagreeable, their eye contact may ruin their chance of convincing someone.

For one study, the authors had participants fill out surveys of their political views and then watch a handful of videos of speakers discussing “hot-button” political issues, some of them looking into the camera and some looking away. The participants were allowed to look wherever they wanted, and the researchers used eye tracking software to see how often the participants gazed into the eyes of the speakers. They then measured how convinced they were by the speaker’s points.

The participants tended to look in the eyes of speakers whose views they shared more. This suggests a confirmation bias in the idea that people who use eye contact are more persuasive—according to this study, eye contact seems to occur more often when the person listening is already generally on board with what the speaker is saying. Participants also tended to look at a speaker’s eyes more when the speaker was looking away.

However, the longer a viewer spent looking at a speaker, especially if the speaker was looking at them directly, the less the viewer was persuaded by the speaker’s points. The effect was more pronounced for issues on which the viewer either opposed the speaker or had no opinion.

In the second study, the researchers presented participants with videos of a speaker they disagreed with on some issue, with some instructed to look at the speaker’s eyes and others his mouth. Again, the researchers tracked the participants’ eyes and gave them questionnaires on their beliefs before and after the videos to see how their views had changed.

The researchers found that viewers who were allowed to look at the speaker’s mouth rather than his eyes ended up more persuaded by what he was saying than participants who had been made to look him in the eyes. Eye contact seemed to have negatively affected the speaker’s ability to be convincing.

The authors suggest that their findings run counter to the oft-repeated advice to look people in the eyes—eye contact is not always persuasive. This may have its roots in evolution. Between animals, eye contact is sometimes “competitive or hostile,” signifying aggression, conflict, and an opponent’s need to prepare to defend rather than an attempt to win someone over or to your side of an argument. “The very experience of meeting the gaze of a disagreeing other… creates a social dynamic characterized by resistance to persuasion,” write the researchers.

The scope of the study was small and conducted only on university students, and the authors acknowledge that the reasons for the lack of attitude changes and behaviors in the two studies may not be linked. They further note that eye contact has a number of social uses beyond persuasion, like signaling “openness to approach and trust.” But when it comes to being convincing, the solution to persuasiveness problems may not be so simple and may even be worsened by an unflinching gaze.

Psychological Science, 2013. DOI: 10.1177/0956797613491968 (About DOIs).