If the image above makes you feel slightly uneasy or completely grossed out, congratulations! You're likely experiencing some degree of trypophobia: an intense fear of clusters of small holes.

While in the vast majority of situations, clusters of small holes aren't exactly life-threatening, this irrational fear is said to affect around 15 percent of people worldwide.

But here's the thing: trypophobia isn't even a real, medically recognised phobia. It's even less legitimate than cyclophobia, a fear of bicycles. So why do so many of us feel something when we see a surinam toad sprouting live babies out of its back?

As this episode of SciShow explains, trypophobia is not yet recognised as a legitimate phobia, and has actually only come into public consciousness very recently. In the mid-2000s, Internet users started getting a kick out of posting things with clusters of small holes in them, and then everyone kind of went nuts.

This has been going on for the past decade, so a couple of researchers from Essex University in the UK decided to figure out once and for all if this irrational fear has some kind of psychological validity.

After showing participants a bunch of benign, inoffensive pictures, and then pictures of things known to gross people out, they found that the pictures that elicited the strongest negative response all shared a common, underlying mathematical structure. 

"Namely, they featured lots of small, highly contrasting details, like stripes, dots, or holes, that were spaced apart in fairly close, regular patterns," says Michael in the video above.

"For example, in [a] lotus pod, there's a high contrast between the dark holes and the light surface, and the holes are spaced evenly enough to highlight those details, while creating a repeating sequence that apparently makes some people want to puke."

The researchers suspect that these patterns relate to things we see in venomous animals, such as the blue-ringed octopus, and certain spiders and snakes, and hence trigger something in our subconscious brains that tells us we could be looking at something dangerous or life-threatening. 

Alternatively, clusters of small holes could be reminding us subconsciously of infectious diseases or skin conditions such as rashes and boils - things we definitely want to stay far away from. 

But another explanation for the recent rise in trypophobia could be that it's an 'emotional contagion', which means you might not have had trypophobia until 5 minutes ago when you started reading this article. How does that work? I'll let Michael explain in the SciShow video above, but just remember - that Swiss cheese might be unnervingly holey, but it can't hurt you. It's just cheese.