"Note that the word 'mute' is regarded by linguists as an onomatopoeic formation referring not to silence but to a certain fundamental opacity of human being, which likes to show the truth by allowing it to be seen hiding."
—Anne Carson

In its most basic form Selective Mutism is a severe fear of speaking to others.
Just like some people have a fear of spiders or snakes or heights, some people have a fear of speaking to others. Sometimes this fear is in regards to certain people. Other times the fear is about particular situations. For the most part, Selective Mutism (SM) first manifests itself in preschool or early elementary school. This is the first time when a child is routinely put in a position where there is an expectation to speak and have an "answer." The majority of people diagnosed with Selective Mutism are also diagnosed with Social Anxiety concurrently or later in life.
The anxieties are sometimes not only in regard to verbal communication, but other types of communication as well. When I was young in school I would not speak to anyone, participate in class, sit at my desk, show much emotion, drink, eat, or use the bathroom. I would become paralyzingly afraid of anything that required me to ask for something or be the focus of a situation, no matter how small.

In no way was any of this willful. I wanted to be able to speak and be a normal kid like everyone else. I would just get so tensed up that the words would float away and my mouth was glued shut.
Most of the common fears people have are generally irrational in nature. For example, I'm deathly afraid of spiders. I flip out when I see one in person or even a picture of one. What is the rationale to being afraid of a picture of a spider? I know the spider isn't real. It can't jump out of the photograph, let alone hurt me. If you asked me why I'm afraid of spiders, I wouldn't have an answer for you.
I like to think of SM the same way I think about other fears. SM is generally based on an irrational fear of other people. Just think of your greatest fear. I bet you are getting anxious just thinking about it. The feeling I get when I see a spider is the same as the one I got when I couldn't speak to people. The adrenaline rush that the body gives is the same response no matter the fear, just the severity changes.

The exact causes of Selective Mutism are not really known, but there seems to be both "nature" and "nurture" factors that contribute to it. I have a long history of mental health issues in my family and I have no doubt that my SM stems somewhat from that. My brain is hardwired to be more reactive to certain situations and have this irrational fear of other people.
However, there are some aspects of SM that are learned behaviors. I like to think of Selective Mutism as not the anxiety specifically, but more of a way that the body uses to cope with it.
Imagine a mother and a 4-year-old boy going into a store to buy ice cream. The boy reluctantly goes up to the counter with his mother. The person behind the counter asks the boy whether he would like a cup or a cone. The boy freezes up, doesn't say anything, and stares at his mother. He is getting visibly upset and the mother notices. She understandably doesn't like seeing her child afraid and decides to step in. She directly asks the boy if he would like a cone and he nods his head. This process continues two more times until the boy gets his vanilla cone with chocolate sprinkles.

 

n this example, the boy gets out of the situation causing him anxiety, the mother is able to "rescue" her child, and both feel much better. However, both the boy and the mom learn a quick way to lessen both of their anxieties. The whole process is even somewhat rewarding to the child because he got out of the anxious situation by not speaking and got an ice cream. As this continues over most interactions in which the boy is expected to speak, this becomes a learned behavior that is practiced over and over again. He learns that his anxieties can be dramatically lessened by not speaking. When we take into account interactions with family, friends, classmates, teachers, and strangers the number of avoided situations becomes massive.
If we take an average school day of six hours and say there is one missed interaction every minute, we get 360 missed interactions per day. In an average school year of 180 days there were 64,800 times that the boy "practiced" not speaking (and this is just during school hours!). If anyone practiced anything 65,000+ times, I bet they would be pretty good at it.


Behavioral treatment of Selective Mutism is about reversing these habits of avoidance. The goal of which is to practice speaking and confront what is anxiety provoking. It is best to start treatment with an expert in SM as soon as possible. The longer the child goes without treatment the more times he or she practices not speaking, and the harder it becomes to reverse it. The opposite is usually true as well with treatment being easier for younger kids for a variety of reasons. It is extremely rare for a child to just outgrow their SM. Left untreated symptoms will persist into teenage years and even adulthood.
The good news is that there are many proven methods to helping kids with SM get over their fears and live normal lives. I have gotten over my SM in practically all situations. The anxieties still persist somewhat, but I have learned other ways to cope with them.