Behaviors and disorders can be broadly classified according to individual reactions to stressors, social adjustment and ability to understand others’ emotions. Without intervention, there can be long-term consequences within social, school and later professional environments. They can be understood this way:
Internalizing behaviors and disorders are characterized primarily by processes within the self, such as anxiety, depression, social withdrawal and somatization (the expression of psychological disturbance in physical symptoms). Here, we have divided internalizing disorders into two categories:
ANXIETY-BASED DISORDERS
MOOD AND EATING DISORDERS
Externalizing behaviors and disorders are characterized primarily by actions in the external world, such as acting out, antisocial or oppositional behavior, hostility, aggression and delinquent behavior. Under externalizing disorders, we include:
ATTENTION AND HABIT DISORDERS
BEHAVIOR (HYPERACTIVE, INPULSIVE, DISRUPTIVE) DISORDERS
Internalizing and externalizing problems are the most common mental health problems, with prevalence rates of 10% among children and 14% among adolescents.
Over the course of development, gender differences occur for the prevalence rate of emotional problems and behavior problems:
- While boys show higher rates of internalizing symptoms during childhood, an increase in internalizing symptoms is reported for teenage girls and young women with greater long-term stability.
- Externalizing symptoms are in general more common among boys, have an earlier onset in childhood and show higher persistence rates with more unfavorable courses.
The developmental dynamics of when both internalizing and externalizing symptoms are present (comorbidity) are not yet well understood. High rates of comorbidity are observed among the following problems: aggression/oppositionality, hyperactivity/inattention, anxiety and social withdrawal symptom.
Internalizing—externalizing profiles
A 2016 study of 336 children from a low-income, urban community, over three years from Kindergarten through second grade, was published in 2016 by Cambridge University Press. The children —64% male, 70% African American, 20% Hispanic—were selected based on a range of high-to-low aggressive/oppositional behavior problems at school. The study found four symptom profiles (% rounded):
- Comorbid internalizing and externalizing (50% of total number of children in each year)
- Internalizing (18%)
- Externalizing (22%)
- Well-adjusted (10%)
Internalizing children had a 20% probability of moving to the well-adjusted profile by the following year. In contrast, externalizing children had a 25% probability of transitioning to the comorbid profile.
These results are consistent with the hypothesis that a common vulnerability factor contributes to developmentally stable internalizing–externalizing comorbidity, while also suggesting that some children with externalizing symptoms are at risk for subsequently accumulating internalizing symptoms.