Clusters of holes, such as those in a lotus seedpod, induce strong discomfort. This is called ‘Trypophobia’. Recently, some researchers addressed what trypophobia is and try to form theories on it. We overviewed the previous studies of trypophobia that have published and presented up to now, and discussed the mental mechanism. Moreover, this article is aimed to ignite future studies of trypophobia by pointing out some unsolved issues and proposing potential solutions.