. There is a hierarchical variation among those suffering from this disorder: some people participate fully in activities and appear social but don't speak, others will speak only to peers but not to adults, others will speak to adults when asked questions requiring short answers but never to peers, and still others speak to no one and participate in few, if any, activities presented to them. In a severe form known as "progressive mutism", the disorder progresses until the sufferer no longer speaks to anyone in any situation, even close family members
Onset of selective mutism may occur as early as school age but generally occurs by mid adolescence following a childhood history of social inhibition or excessive shyness.
The onset of selective mutism is often abrupt, occurring after a stressor or humiliating social experience and typically occurs when a child first attends school (either kindergarten or preschool). Over time, anxiety levels tend to increase as children do not "grow out of" selective mutism. Selective mutism persists as low self-confidence, shyness, and discomfort in social situations, often persisting into adulthood when speaking in public is required
The etiology of selective mutism is multifactorial. Some children develop selective mutism after a stressor such as illness, separation from their caregiver, or other traumatic experiences such as abuse or neglect and bullying can especially contribute risk and also occur related to the lack of a large supportive peer group. This is because youth with selective mutism are not as likely as "normal" unaffected peers to be protected by peer bystanders from being targeted and victimized by bullying.