Incest between adults and children is a form of child sexual abuse . This form has been shown to cause one of the worst forms of childhood trauma , a trauma that often causes serious and long-term psychological damage , especially in the case of parental incest . Incest between adults and those under the age of majority or age of consent is considered a form of child sexual abuse that has been shown to be one of the most extreme forms of childhood abuse , often resulting in serious and long-term psychological trauma , especially in the case of parental incest .