What causes trypophobia?

Trypophobia is the phenomenon in which individuals report a range of aversive responses when seeing clusters of small holes. Since the phenomenon was first described in the peer-reviewed literature in 2013, approximately 60 papers have appeared directly concerned with the condition. There have also been hundreds of news articles in both online and print media. In the present review of the literature, we examine why trypophobia is likely to occur. Four explanations have been posited in the past decade. These state that the stimuli (1) induce cortical hyperexcitability via the image statistics they possess, (2) signal the presence of a dangerous/poisonous animal, (3) cue the observer to the presence of disease and (4) are aversive due to a form of social learning. We argue that the available evidence points to the disease avoidance hypothesis as the most likely account of the phenomenon.