Even though we could translate the English adjective “creepy” as “chilling” (or “horrifying”, to name two common examples) we would be incurring a gross distortion.
It is impossible to define why something is “creepy”, however, we could all identify it as something that produces a combination of fear with something else; something indefinable.
Fear is evolutionarily logical. I mean, being afraid of the night, of insects, of predators, is useful for any species; even for us.
But what happens when fear is caused by something whose dangerousness is not entirely clear?
Or better yet, when fear occurs in response to something that causes us a mixture of rejection and fascination?
For example, an unconventional doll …

Clearly this is a doll that we would not want to find ourselves in a dark room; however, the fascination is also present.
Why?
Just as our brain cannot diagnose a real danger in these types of objects, our language also runs out of tools, so we appeal to the “creepy”; that which no one can define with precision but which we all understand.
But what causes something to be “creepy”?
The equation, formulated by Sigmund Freud in his 1919 essay: The Sinister (Das Unheimliche), concerning the ominous, could be translated to “creepy” as follows:
“Creepy occurs when something is simultaneously usual and unusual.”
There will be those who maintain that true fear occurs in the face of death, wars, famines, disease; which is strictly true. However, none of those things is “creepy”.

So should we make a difference between “something creepy” and something that produces fear?

Stephen King defines three types of reactions linked to fear:

1)Gross-Out, which occurs in front of something disgusting, sick, disgusting, morbid; for example, someone eating their own guts or excrement.

2) Horror, which for Stephen King can only occur in the face of the supernatural, the inexplicable; for example, feeling a cold, autonomous hand crawl under the covers.

3) Terror, basically “something creepy”; for example, the fleeting shadows that cross the corner of the eye, the vague sensation (not the certainty) that someone is behind us but disappears the moment we turn around.

Beyond the views of Stephen King, who portray fear from a literary rather than anthropological aspect, “creepy” is defined by the ambiguous, the uncertain, the vague.

That is why masks scare us, according to Claude Levi-Strauss, because the elimination of facial features prevents us from determining whether we are facing a threat or not.
And if we talk about masks, the clowns take the first prize.

Clowns scare us not only because they wear a make-up mask, but because that mask simulates a state of static, immobile joy, under which we suspect something horrible.
This is the ambiguity that sustains “creepy” and differentiates it from objective fear, even when it is produced by causes that we suppose to be supernatural.

We could also risk that “creepy” is never complete or absolute; it is always “almost something,” for example, like the effect discovered by robotics expert Masahiro Mori, known as Uncanny Valley.

Humans seem to react favorably to anthropomorphism, as long as it doesn’t reach alarming levels of similarity to us. In other words, something becomes “creepy” when it is “almost” identical to us.
C3P0 seems very nice to us, perhaps because its form is human and pleasant, but if the similarities increase, any robot becomes “creepy”.

That’s why animated movies for boys rarely flirt with Haunting Valley. Children react very favorably to anthropomorphism, but with real horror if things get out of hand.
In short, “the creepy” inhabits that ambiguous region between the usual and the unusual, between what we know but which at the same time causes us an inexplicable rejection. “Creepy” is the “almost”, what could be, what perhaps is, what borders on horror without actually being it.

http://dimidesan.com/index.php/2021/10/06/horror-movies-and-health/

http://dimidesan.com/index.php/2021/10/04/horrors-sweet-pleasure/