People cry when reunited with loved ones, scream on getting good news and pinch cute babies' cheeks. Yet why do such positive experiences elicit these “negative” reactions? New research suggests we may do it to calm ourselves down so we can handle situations better.

Oriana Aragón, a psychologist at Yale University, and her colleagues surveyed 143 adults about how they tend to react to good and bad experiences. Then they showed the subjects pictures of babies that varied in terms of their “cuteness,” based on earlier research that suggests that babies are considered cuter if they have bigger cheeks and eyes and smaller chins and noses. The researchers then asked the subjects how they felt about the babies and how they wanted to interact with them.

Aragón and her colleagues found that the cuter the babies were, the more likely the subjects were to be overwhelmed by positive feelings on seeing their pictures. Subjects were also more likely to want to be “playfully aggressive” with the cuter babies, for instance, by pinching their cheeks. In a follow-up study, Aragón found that when subjects said they wanted to be playfully aggressive with cute babies, they calmed down more quickly—they became more emotionally neutral several minutes later compared with subjects who did not want to be playfully aggressive. “We have the first evidence that these negative expressions may help in regulating overwhelming positive emotions,” Aragón says.

But why would we want to regulate our positive emotions? Research suggests that feeling “too positive” can interfere with decision making and cause people to neglect environmental threats and act impulsively. So if a father who is overwhelmed with joy at the sight of his adorable daughter feels the need to nibble on her toes, the reaction could ultimately be in both their best interests. “The baby is served by these expressions if the expressions calm down the adult who is overwhelmed,” Aragón says.