Anxiety disorders are the most common psychological disorder in the U.S., affecting 18 percent of the adult population. Social anxiety disorder (SAD) is the third-most-common psychological disorder, affecting 15 million men and women in the U.S. The DSM-5 defines social anxiety as the "persistent fear of one or more situations in which the person is exposed to possible scrutiny by others and fears that he or she may do something or act in a way that will be humiliating or embarrassing."
Those who are shy, if not socially anxious, tend to experience social situations in a more reserved, tense and uncomfortable manner, especially when meeting new people. It may take longer to open up and share, which can affect one's ability to form close relationships.