What are the causes of fear of public speaking?

Glossophobia, or the fear of public speaking, is most often caused by the perception of negative or judgmental scrutiny from others. This perception results in the cognitive or physiological anxiety reactions common in people with stage fright.

When a person has a cognitive anxiety reaction, they become mired in negative thought patterns. These thoughts center around the likelihood of a negative outcome (this will go terribly) and over-generalizing (this speech was bad, so every speech will be bad).

A physiological anxiety reaction can cause intense physical feelings like sweaty palms, fast heart beat, dizziness and shortness of breath. When a speaker has a has a physical anxiety reaction once, it is more likely to happen again, creating a pattern of automatic behavior that further feeds the public speaking fear.