By Charlotte Evans
Everyone is scared of something, but few have a true phobia. The official diagnostic manual for mental disorders (DSM-5) classifies phobias as an anxiety disorder characterized by an intense fear of a specific thing or situation, with common phobias being spiders or heights (American Psychiatric Association, 2013). Is your fear that of tiny holes? Does looking at sponges, honeycomb, or diseased tissue make you want to run away? If so, your fear might be classified as trypophobia! This hatred of non-threatening groups of circles or pores has gained attention over the past few years in popular media like Black Panther (Killmonger’s scars) and American Horror Story (Wagner, Croley, & Wilson, 2018).
Several theories have been thrown around about the origins of this disorder. A prominent one cites an evolutionary basis in our natural fear of venomous snakes or spiders which often have spots that might elicit a trypophobic reaction. Similarly, parasitic infections produce hole-riddled tissue which historic humans had good reason to avoid. Other theories point to the spatial frequency of the pattern, rather than the holes themselves, as being uncomfortable to look at. However, a recent study investigates whether trypophobia is truly a “phobia” at all (Ayzenberg, Hickey, & Lourenco, 2018).
This innovative research on trypophobia used pupil dilation as a proxy to examine the fear and disgust responses to particular stimuli (Ayzenberg et al., 2018). Both physiological responses produce an aversive behavior, but fear is rooted in danger and activates the sympathetic nervous system (making us want to flee) while disgust is associated with contamination and the parasympathetic branch of the nervous system. These two systems work in opposing ways depending on the needs of the organism, and can be observed, and thus studied, in the eye. When the pupil grows in size, more light is let in and the body prepares to fight or flight; when the pupil contracts, the parasympathetic nervous system dominates and we relax.
This study tested trypophobic, fearful/threatening, and neutral images on a cohort of college students. It had previously been found that even non-trypophobic individuals normally have a mild aversion to trypophobic images, allowing the researchers to measure all participants’ responses by briefly presenting each image and recording the change in pupil size from the student’s baseline. It was found that hole-filled images were associated with the smallest pupil size, as would be expected from parasympathetic activation. They followed up this experiment with another that additionally measured self-reported level of arousal after each image and non-hole, patterned images. The found that the spatial frequency of the image correlated to pupil size, the fearful stimuli produced greater arousal than the holes, and again that hole stimuli were associated with smaller pupil size than fearful stimuli. Importantly, they found that the hole stimuli elicited smaller pupils than the patterned controls (Ayzenberg et al., 2018).
The takeaway from this innovative approach to phobia research is that, scary as they may seem, images of many tiny holes are not frightening, but disgusting. We cannot control our sympathetic and parasympathetic responses, so measuring pupil size serves as an objective measure of arousal level. Furthermore, this study also somewhat refuted the spatial frequency hypothesis for trypophobia because the explicitly trypophobic images produced a stronger parasympathetic response than patterned stimuli of a similar spatial frequency. The authors thus argue that it is the content of the image that produces this disgust response. Trypophobia is not the only “phobic” disorder with disgust as it’s aversive driver. While snakes and spiders elicit a more typical fear response, blood-injection phobia generates a disgust response, as does OCD (Ayzenberg et al., 2018). All phobias can be extremely debilitating, but traditional phobias can be excellent subjects of investigation for anxiety research and for developing new methods of therapy. New insights into the neuroscience behind different kinds of phobias may help us more effectively study and treat them. This includes trypophobia, which is a very real aversion to innocuous stimuli that warrants more study, regardless of whether these tiny holes gross you out or scare your socks off.
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). https://doi.org/10.1176/appi.books.9780890425596
Ayzenberg, V., Hickey, M. R., & Lourenco, S. F. (2018). Pupillometry reveals the physiological underpinnings of the aversion to holes. PeerJ, 6. https://doi.org/10.7717/peerj.4185
Wagner, K. D., Croley, J. A., & Wilson, J. M. (2018). Trypophobia, skin, and media. Dermatology Online Journal, 24(11).