Most people, from those who are fond of living alone to the rich and famous, probably have experienced feelings of shyness at various times in their lives. Physiological symptoms may include blushing, increased heart rate, sweating, and shaking. Just as these outward manifestations vary in type and intensity from person to person, so do the inner feelings. Anxious thoughts and worries, low selfesteem, self-criticism, and concern over a lack of social skills, real or imagined, are common. Nevertheless, the causes of shyness are not known. Some researchers believe it results from a genetic predisposition. Others theorize that uncommunicative parents restrict a child's development of the social skills that compensate for discomfort caused by new experiences and people, resulting in shyness. Variously, it has been considered a symptom of social phobia or a simple characteristic of introversion. Psychological research that follows large numbers of children from very early childhood to adulthood has found that a tendency to be shy with others is one of the most stable traits that is preserved from the first three or four years of life through young adulthood. Learning or improving social skills through self-help courses or formal training in assertiveness and public speaking are some of the methods used to diminish the effects of shyness.