Watching scary films, playing scary games, driving on a large rollercoaster, are few of the acts that make people frightened and shocked but on other hand, people like this type of entertainment.  The meaning is that the sudden excitement of the obscure lifts up heart rate and increases adrenaline, and as long as doing these frightening acts, if the person recognizes that they are not true danger, they can be processed, laughed about and enjoyed.  Young ones, even if are not completely alert of the cause of this type of amusement, generally find it amusing, but on other hand there are some figures conceptualized to be entertaining, but however they scare with their appearing.  

One image of this type is the clown.  They are funny entertainers, conventionally characterized by the concept of the Circus clown, with coloured wigs, heavy makeup, eccentric clothes, extremely large shoes, red-nose…  They say jokes, do some foolish acts that many times call for powerful physical disposition and dozens hours of preparation.  Even if they are conceptualized as entertaining image that makes young ones and grownups smile, a big group of people, young and adults, finds clowns very frightening.  Agreeing to the analyses, about 20 to 30% of the whole population find clowns threatening.

In psychology this kind of fear is called Coulrophobia and it could result with panic attacks, anxiety and alike phobic reactions.

There are many hypotheses why many people find clowns frightening.  Professionals state that is related with some childhood trauma.  They emphasise that first touch with circus could be pretty disturbing for a child.  There is a perceptible overloading with strange spectacles, sounds and smells so a child could without difficulty become affected by the surreality of all that.

Also there is a conception about the role that clowns have in society.  Young ones are directed that they have the right to appear as young ones and adults have the duty to act like adults.  In this situation there is a difference because clowns are stimulated to be adults acting like young ones.  Also here is the alarm from harassment by a masked or disguised aggressor.  Feeling humbled or ridiculed in community could be a very painful happening for some people, even if it's done in the name of comedy.

Another cause could be the fact that clowns are frequently depicted as emotionally weak or psychotic.  They are qualified as emotionally conflicted persons that give a wrong idea of happiness as long as hiding big personal pain.  

To all this could be added the belief of a "killer clown", used in horror films and stories dozens times.  Apparently the photographs of the serial murderer John Wayne Gacy, dressed as a clown, which have been circulated many times, also took part in tagging of the clowns as frightening images.