Social anxiety disorder, also known as social phobia, is a mental illness. It belongs to a group of mental illnesses called anxiety disorders. People with social anxiety disorder feel very nervous and uncomfortable in social situations like meeting new people.

Why do I get nervous before social events?

Social anxiety is a result of the fear of a possibility that we will not be accepted by our peers. Its the fear of negative evaluation by others, and that is [part of] a very fundamental, biological need to be liked. Thats why we have social anxiety.