I went to a birthday party recently with my 3-year-old son. The party had it all: moon bounce, cake, face painting and — you guessed it — a clown. My son happens to be scared silly of clowns, so much so that I had to cajole him for 30 minutes in the driveway. And he wasn't the only one who was frightened. There were at least four or five other kids who were similarly terrified. And I have to admit, I wouldn't want to be alone in a room with a party clown. They just make me nervous. But why is that?

Turns out being scared of clowns is relatively common. Coulrophobia is the intense fear of clowns. And though I can't say my son has it (he's also irrationally afraid of automatic doors and worms), I can definitely understand why. And so can psychologists.

Elan Barenholtz, Ph.D., associate professor of psychology at Florida Atlantic University, explains the phenomenon. "People find any concealment of someone's true face, such as a mask, unsettling because it, masks a source of communication of their emotional state and identity," he says. "We look to the face to determine if someone is trustworthy or not, angry or happy, or someone we know or don't know — heavy face makeup, especially with a fake painted smile, obscures a lot of this information."

Joseph Grimaldi The actor Joseph Grimaldi as Clown in the pantomime 'Harlequin and Friar Bacon' by Bonnor and O'Keefe staged at the Theatre Royal, Covent Garden London in 1820. Detail from hand-coloured etching. (Illustration: George Cruikshank [public domain]/Wikimedia Commons)

The persona of the "scary clown" is not one manufactured by my son. In fact, some will say that the scary or sad clown is as old as clowns themselves. One of the first and most famous clowns, Joseph Grimaldi (shown above), used to say "I am GRIM-ALL-DAY so you can laugh at night." It was well known that his personal life was as tragic as his stage character was jovial. Grimaldi was raised by a tyrannical stage father, his first wife died during childbirth and his son drank himself to death at the age of 31.

In France, a famous makeup-clad clown who delighted French audiences named Jean-Gaspard Deburau actually killed a young heckler in 1836. Though he was later acquitted of murder, his reputation — and that of the clown — was tarnished forever.

IT Stephen King Horror Movie In Lego Stop Motion Parody 2 If you don't like clowns, Stephen King's 'It' in Lego Stop Motion is probably too much. (Photo: wahyu purnawan [CC BY 2.0]/Flickr)

Fast forward to 20th century America where John Wayne Gacy, a registered clown who entertained kids for year under the stage name Pogo, sexually assaulted and murdered more than 35 young men in the Chicago area in the 1970s. He was tried, convicted and sentenced to death. The persona of the scary clown has been perpetuated by horrific turns in books and movies like Stephen King's "It," and "Clownhouse," and more recently, Heath Ledger's iconic turn as The Joker in "The Dark Knight."

Stoking the flames of clown fear may be another psychological phenomenon at work, something called the "uncanny valley effect." What is it exactly? "It's a tendency for people to dislike faces that are close to human looking but not quite normal," says Barenholtz. "Clowns may elicit similar emotional responses because they look human but are not quite."

All that being said, clowns don't have to be sinister. In fact, I can anecdotally say that their presence is still enjoyed by most kids at a birthday party. And more importantly, clown doctors have been proven effective at reducing kids' anxiety in hospitals, which in turn can help them on their path to treatment and recovery. As the beloved Patch Adams famously said, "Being happy is the best cure of all diseases."

Why are some people terrified of clowns?
For some of us, these creepy jesters are no laughing matter.