Separation anxiety is a normal stage of development for infants and toddlers, where young children often experience a period of separation anxiety, but most children outgrow separation anxiety by about 3 years of age. However, in some children, separation anxiety is a sign of a more serious condition known as separation anxiety disorder (SAD), starting as early as preschool age. SAD is an anxiety disorder that causes a child to suffer from feelings of extreme worry when apart from family members or other close people. A child with SAD worries a lot about being apart from family members or other close people and has a fear of being lost from their family or of something bad occurring to a family member if he or she is not with the person. Symptoms of SAD are excessive for the developmental age and cause significant distress in daily functioning. Symptoms may include fear of being left alone, nightmares, bedwetting, and following the caregiver around the house. Separation anxiety disorder can also occur in teenagers and adults, causing significant problems leaving home or going to work. The disorder manifests with improper intensity at an inappropriate age or in an inappropriate context. The causes of SAD are believed to be both biological and environmental factors, including a tendency to be anxious, an imbalance of two chemicals in the brain, and learning anxiety and fear from family members and others. Treatment for SAD includes cognitive-behavioral therapy, medicines, family therapy, and school input.