A U.S. study of 770 adolescents looked into the risk factors for the development of social anxiety disorder in this group. They found that social anxiety disorder remained constant over time. Childhood negative effect, shyness and chronic illness during childhood were all associated with adolescent social anxiety. Childhood shyness was more likely to turn into social anxiety disorder in girls than in boys. Childhood shyness and childhood chronic illness combined had a much stronger impact on the risk of adolescent social anxiety disorder than their individual effects.
Hayward, Chris ... [et al] - The developmental psychopathology of social anxiety in adolescents Depression and Anxiety, 2008, 25(3), 200-206