At this time, due to the immature emotion regulation abilities of adolescents, long-term exposure to these stressors causes difficulty in coping with negative emotions, leading to malfunction of reward system (i.e., abnormal secretion of endorphins, dopamine, oxytocin, etc.)or the abnormalities in the hypothalamic–pituitary–adrenal (HPA) axis, which may provide the environment for the emergence of depression (7, 8). This evidence concerns the gene OXT and major depressive disorder.