Dr. Lisa M. Hooper, who headed the Parentification Research Group at The University of Alabama, has defined parentification as "the distortion or lack of boundaries between and among family subsystems, such that children take on roles and responsibilities usually reserved for adults." But Salvador Minuchin only thought that families ran into difficulty when it wasn't clear who was in charge or if the parents abdicated their roles. However, both Ivan Böszörményi-Nagy and Salvador Minuchin believed that in extreme cases parentified children can become so overburdened that their own childhood needs go unmet.
Some researchers have further classified parentification as either emotional or instrumental. Emotional parentification is when a child fills the psychological or emotional void left by a parent. Instrumental parentification is when a child takes on parental responsibilities. While instrumental parentification can produce a sense of accomplishment for having contributed to the family, emotional parentification often leads to the suppression of the child's own needs in order to meet the parent's needs. Hence, emotional parentification is considered to be more harmful than instrumental parentification. But regardless of which type, problems will likely develop if parentification continues indefinitely.
With respect to incest, parentification is known to be prevalent in families which engage in overt and/or covert incest. While evidence of instrumental parentification may be lacking in such families, the presence of emotional parentification is well-established.