Separation anxiety disorder (SAD) is an anxiety disorder in which an individual experiences excessive anxiety regarding separation from home and/or from people to whom the individual has a strong emotional attachment (e.g., a parent, caregiver, significant other, or siblings). Separation anxiety is a natural part of the developmental process. It is most common in infants and little children, typically between the ages of six to seven months to three years, although it may pathologically manifest itself in older children, adolescents and adults. Unlike SAD (indicated by excessive anxiety), normal separation anxiety indicates healthy advancements in a childs cognitive maturation and should not be considered a developing behavioral problem.According to the American Psychiatric Association (APA), separation anxiety disorder is an excessive display of fear and distress when faced with situations of separation from the home and/or from a specific attachment figure. The anxiety that is expressed is categorized as being atypical of the expected developmental level and age. The severity of the symptoms ranges from anticipatory uneasiness to full-blown anxiety about separation.SAD may cause significant negative effects within areas of social and emotional functioning, family life, and physical health of the disordered individual. The duration of this problem must persist for at least four weeks and must present itself before a child is eighteen years of age to be diagnosed as SAD in children, but can now be diagnosed in adults with a duration typically lasting six months in adults as specified by the DSM-5.
Children with BI are at a higher risk for developing a mental disorder, particularly anxiety disorders, than children without BI.Separation anxiety is normal in young children, until they age 3–4 years, when children are left in a daycare or preschool, away from their parent or primary caregiver.To be diagnosed with SAD, one must display at least three of the following criteria:

Recurrent excessive distress when anticipating or experiencing separation from home or from major attachment figures
Persistent and excessive worry about losing major attachment figures or about possible harm to them, such as illness, injury, disasters, or death
Persistent and excessive worry about experiencing an untoward event (e.g., getting lost, being kidnapped, having an accident, becoming ill) that causes separation from a major attachment figure
Persistent reluctance or refusal to go out, away from home, to school, to work, or elsewhere because of fear of separation
Persistent and excessive fear of or reluctance about being alone or without major attachment figures at home or in other settings
Persistent reluctance or refusal to sleep away from home or to go to sleep without being near a major attachment figure
Repeated nightmares involving the theme of separation
Repeated complaints of physical symptoms (e.g., headaches, stomachaches, nausea, vomiting) when separation from major attachment figures occurs or is anticipated

Classification
Separation anxiety is common for infants between the ages of eight and fourteen months and occurs as infants begin to understand their own selfhood—or understand that they are separate persons from their primary caregiver.