Here's why people are really afraid of clowns

Coulrophobia—the fear of clowns—is a very real phobia among children and adult across the world. But what makes them so scary to some people? Psychologists from the University of South Wales devised a study to scientifically suss out the root of the fear. Of nearly 1,000 people aged 18 to 77 that they surveyed, 53.5% were frightened of clowns "at least to some degree." Those 53.5% then received a follow-up questionnaire to get at the origin of their fear. Unsurprisingly, the least identified explanation was that the respondents had a prior frightening experience with a clown. Also not surprisingly, many people's coulorophobia is fueled by scary clowns in popular culture. From Science Alert:

However, some people are afraid of Ronald McDonald, the fast food chain mascot, and he is not meant to scare you. This suggests there might be something more fundamental about the way clowns look that unsettles people.

In fact the strongest factor we identified was hidden emotional signals, suggesting that for many people, a fear of clowns stems from not being able to see their facial expressions due to their make-up.

We cannot see their "true" faces and therefore cannot understand their emotional intent.

So, for example, we don't know whether they have a frown or a furrowed brow, which would indicate anger. Not being able to detect what a clown is thinking or what they might do next makes some of us on edge when we are around them.

"Fear of clowns: An investigation into the aetiology of coulrophobia" (Frontiers in Psychology)