Child abuse and neglect have been shown, in some cases, to cause important regions of the brain to fail to form or grow properly, resulting in impaired development. Structural brain changes as a result of child abuse or neglect include overall smaller brain volume, hippocampal atrophy, prefrontal cortex dysfunction, decreased corpus callosum density, and delays in the myelination of synapses. These alterations in brain maturation have long-term consequences for cognitive, language, and academic abilities. In addition, these neurological changes impact the amygdala and hypothalamic-pituitary-adrenal (HPA) axis which are involved in stress response and may cause PTSD symptoms. Poor physical health. In addition to possible immediate adverse physical effects, household dysfunction and childhood maltreatment are strongly associated with many chronic physical and psychological effects, including subsequent ill-health in childhood, adolescence and adulthood, with  higher rates of chronic conditions, high-risk health behaviors and shortened lifespan. Adults who experienced abuse or neglect during childhood are more likely to have physical ailments such as allergies, arthritis, asthma, bronchitis, high blood pressure, and ulcers. There may be a higher risk of developing cancer later in life, as well as possible immune dysfunction. Exposure to violence during childhood is associated with shortened telomeres and with reduced telomerase activity. The increased rate of telomere length reduction correlates to a reduction in lifespan of 7 to 15 years.
In 1995, APSAC defined it as: spurning, terrorizing, isolating, exploiting, corrupting, denying emotional responsiveness, or neglect" or "A repeated pattern of caregiver behavior or extreme incident(s) that convey to children that they are worthless, flawed, unloved, unwanted, endangered, or only of value in meeting anothers needs"
In the United States, states laws vary, but most have laws against "mental injury"
Some have defined it as the production of psychological and social defects in the growth of a child as a result of behavior such as loud yelling, coarse and rude attitude, inattention, harsh criticism, and denigration of the childs personality. Other examples include name-calling, ridicule, degradation, destruction of personal belongings, torture or killing of a pet, excessive criticism, inappropriate or excessive demands, withholding communication, and routine labeling or humiliation.In 2014, the APA found that child psychological abuse is the most prevalent form of childhood abuse in the United States, affecting nearly 3 million children annually. Research has suggested that the consequences of child psychological abuse may be equally as harmful as those of sexual or physical abuse.Victims of emotional abuse may react by distancing themselves from the abuser, internalizing the abusive words, or fighting back by insulting the abuser. Emotional abuse can result in abnormal or disrupted attachment development, a tendency for victims to blame themselves (self-blame) for the abuse, learned helplessness, and overly passive behavior.