The tendency to avoid or be timid or subdued with unfamiliar children or adults.

Shyness first appears around the first birthday, when the capacity to experience fear to discrepant events matures. During the first year or two children raised under most family circumstances who are extremely shy behave this way because of a temperamental bias to react with withdrawal to unfamiliar events. When the unfamiliar event is meeting a stranger, the child is called shy. However, as children grow, other reasons for shyness emerge and many five and six-year-old children can show shyness without any special temperamental predisposition. Some children are shy because they feel that they are physically unattractive, others are shy because they have failed to attain proper achievement levels in school, and other children are shy because of shame over aspects of their family, including poverty or mental illness.

Kenneth Rubin of the University of...