Selective Mutism (SM) is an anxiety disorder. The World Health Organization classifies it as a type of phobia. Selective Mutism is simply the fear of speaking in specific environments. It is not a result of trauma or a choice made by the child. Instead, it is the result of genetic predisposition combined with a state of fear that is further intensified by various environmental factors.

When a child starts school, it takes about a month to adjust. If this period extends and the child does not speak or speaks very little and quietly, does not respond to questions, does not ask to use the toilet, does not eat, does not drink, and does not participate in play despite being a cheerful child and speaking in places where they feel safe (e.g., at home), then there are strong indications that it is Selective Mutism.