A theory originally put forward by Cole, it proposes humans have evolved to be fearful of such patterns as they are usually seen on poisonous animals or food.

“If you look at animals which are dangerous in this respect, like the poison dart frog, they tend to be covered in high contrast colours. These visual signatures are barely found anywhere else in the natural world,” explains Cole.

“Basically, the idea here is that when you look at a trypophobic image your brain is saying ‘be careful here, this could harm you.’”

Read more about phobias:

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The pathological theory

Like the above, this explanation suggests trypophobia is an evolutionary adaptation: as many skin diseases have trypophobic traits, humans have evolved to pay these patterns attention.

“It follows the thinking that humans have developed a sensitivity towards skin pathology,” says Cole. “In this way, it’s possible that a trypophobic reaction keeps us alert to any illness, either on ourselves or others.”

The visual stress theory

The current favourite of researchers like Cole, this theory proposes, that we can’t quite be sure what causes it – that trypophobia serves no functional purpose and has no solid evolutionary adaptation.

“The neuroscience behind this theory is quite interesting. Recently we used a technique called infrared spectroscopy to examine people with trypophobia – it’s a method that allows you to see where the blood and activity are in somebody’s brain,” says Cole.

“And on seeing trypophobic images, the blood was found towards the back of participants’ brains – it was in the visual areas of the brain, rather than the frontal decision-making areas.”

As Cole says, this may indicate a trypophobic response may not be prompting us to make a decision about how dangerous an object is. “It indicates there might not be an evolutionary reason why we don’t like these images – it may simply just be that the brain doesn’t like it. And we might never know more than this.”

The internet meme theory

What if trypophobia didn’t actually exist at all before it became big in internet forums? What if humans have been trained to think these images are something to fear due to online hype? That’s the explanation some have put forward.

“It’s the whole nature versus nurture argument: are people really born with a revulsion to things like rats? Or are we socially conditioned to be afraid of them?” says Cole.

“As some people argue, isn’t it strange that more people develop phobias of spiders, but not cars, which are more likely to kill you? There’s a massive debate about phobia acquisition here that may never be solved.”

As many review papers have noted, it’s difficult to examine genetic factors from social – no phobia studies have yet been carried out on identical twins raised in different households.

True, in one study six-month-old infants were shown to have slightly higher levels of ‘fight or flight’ chemical norepinephrine when presented with images of snakes and spiders, compared to flowers and goldfish. But this alone does not prove common human phobias and fears are in-built.

“And with trypophobia it’s getting harder to separate nature from nurture, particularly with results. As these images become more popular online, how likely is it you can find an adult that has never seen a trypophobic image before and test them?”

In short, when it comes to trypophobia, it’s getting more and more unlikely we’ll know the hole truth.