Editor’s Note (12/17/18): The published article by Dong & Zhong (2018) highlighted in this post has been retracted by Psychological Science. After the original article was published, a reader detected a critical flaw in the experimental protocol that confounds interpretation of the data. 

Fears come in all shapes and sizes. Some of us are afraid of heights, loud noises, or tight spaces, while others have fears of more specific things like snakes, spiders, or clowns. One fairly universal fear, especially for children but even among adults, is a fear of the dark. Nearly any familiar, comfortable environment—a neighborhood park, your favorite campground, even your own home can feel creepy and threatening. Because we cannot see the real (or imagined) dangers in our midst, we feel vulnerable and exposed. Innocuous things we would otherwise ignore during day can startle or frighten in the dark of night.

Not everything, however, is scarier in the dark. New research by Ping Dong and Chen-Bo Zhong suggests that when the lights are out we are less fearful of contracting a contagious disease. Dong and Zhong evaluated people’s perceived risk of catching the seasonal flu from a coughing, sniffling individual, and found that their fear of contagion diminished in the dark.

Participants first viewed and evaluated a brief, neutral documentary film. Half watched the film with the lights on, and half with the lights off. Each participant sat adjacent to a trained confederate, who intentionally coughed and sniffed during the session. Critically, the confederate made precisely the same number of coughs/sniffles each session, regardless of the lighting. Participants then completed a judgment task in which they estimated the likelihood of contracting six different diseases—one contagious (seasonal flu) and several non-contagious (e.g., skin cancer, diabetes, asthma). Estimates of contracting the seasonal flu were significantly reduced when the lights were dimmed, and this pattern was robust in both a lab manipulation and a real-world classroom setting. It was also observed when the light exposure was reduced by having participants wear sunglasses.

One possibility is that participants tested in the dark were simply less likely to notice the coughing and sniffing behavior of the confederate. To address this possibility, Dong and Zhong asked all participants to report whether they heard someone coughing during the study, and found the same pattern of diminished perception of risk in the dark even when participants who failed to hear the coughing were omitted from analyses.

Instead, Dong and Zhong posit that the reduction in perceived risk of contagion results from changes in construal levels, or the way that we perceive and think about the world. When it is dark, we can see global features (e.g., the figure of a person, the outline of furniture) but not specific details (e.g., the color of a person’s eyes, the fabric on the furniture). Consequently, we are more likely to create global rather than detailed representations in the dark, and this in turn may increase our perceived social distance from others. When we see ourselves as more distant from others, our perception of contagion risk decreases.

To assess this possibility, Dong and Zhong replicated their initial paradigm and included measures of perceived social distance. Participants not only evaluated their risk of contagious disease, but also reported how far away they felt from the coughing confederate. (All participants were seated the same distance from the confederate.) Once again participants tested in the dark reported lower perceived risk of contracting the flu than those tested in a bright room. In addition, visual darkness increased participants’ perceived distance from the confederate, and this increase in distance mediated the reduction in perceived risk of contagion in the dark. Their fear of non-contagious diseases did not depend on the lighting.

Darkness, it turns out, can also reduce the intensity of emotional responses and can promote unethical behaviors, including cheating and selfishness. These findings suggest that the low levels of illumination commonly found in restaurants, cinemas, nightclubs, airplanes, and along highways could elevate the risk of a number of unhealthy or even dangerous behaviors, including failure to wash one’s hands, sexual promiscuity, or an increased likelihood of speeding or drunk driving. Perhaps there is, after all, reason to fear the dark.