Teens display a range of emotional behaviors, and as each child is an individual, those behaviors can differ from one teen to another. Impulsiveness, rebellion, irritability and periods of non-communication are all typical of teens, according to A Parent’s Guide to the Teen Brain website. When a teen fails to show emotion, however, it can mean a problem. A teen who shows little or no emotion might have been abused, be mentally ill, depressed or have a head injury.
In medical terms, a person’s expression of her emotions is known as an affect, according to the Department of Psychiatry and Behavior Sciences at the University of Washington School of Medicine. The affect is not the emotion itself, but a behavior that can be observed by someone else. Anger and sadness are typical examples of an affect. People display a range of affects, as indicated by their facial expressions, voice pitch and the way they move their hands and bodies. Human affects range from normal through restricted to blunted or flat. A restricted affect results in diminished expression of emotional behaviors which becomes more severe in a blunted affect. A flat affect is lack of facial expressions and a monotone voice.
A teen who was sexually or physically abused as a child or is still being abused might develop a number of signs and symptoms. Children need nurturing relationships with their primary adult caregivers to meet their needs for food, warmth, protection and emotional development. Sexual and physical abuse can disrupt these relationships, leading the teen to expect pain or injury from others, creating a pattern of distrust and wariness. Abused children can develop a pattern of denying emotional responses to cope with the psychic pain of being abused, which leads to a blunted affect. Abused teens might also display delinquent behavior, run away, engage in self-harming behaviors or become sexually promiscuous.
Mental Illness and Depression
Mental illnesses such as schizophrenia can cause a blunted affect, according to "The Merck Manual." Although women don’t generally develop schizophrenia until they are in their 20s, male teens can develop symptoms around the age of 18. In addition to a blunted or flattened affect, a teen with schizophrenia could develop psychosis -- a lack of contact with reality -- hallucinations, an inability to think clearly or problems relating to other people. Depression, which can appear in schizophrenia or independently, is another possible source of blunted affect, according to Prevent Child Abuse Vermont.
Head injuries can result in damage to the structures of the brain. In addition to other symptoms, head injuries can also cause depression, which can result in a blunt affect. The frontal lobes of the brain -- located in the area behind the forehead -- are the emotional control center of the brain. The frontal lobes control judgment, impulsivity, social and sexual behavior as well as other behaviors. Patients who have frontal lobe injuries have limited facial expressions because the frontal lobes control expressions, but also have a blunted affect because damage to the brain structure interferes with the ability to express emotions, according to the University of Miami Miller School of Medicine.