Child abuse is a complex phenomenon with multiple causes. Understanding the causes of abuse is crucial to addressing the problem of child abuse. Parents who physically abuse their spouses are more likely than others to physically abuse their children. However, it is impossible to know whether marital strife is a cause of child abuse, or if both the marital strife and the abuse are caused by tendencies in the abuser.
Children resulting from unintended pregnancies are more likely to be abused or neglected. In addition, unintended pregnancies are more likely than intended pregnancies to be associated with abusive relationships, and there is an increased risk of physical violence during pregnancy. They also result in poorer maternal mental health, and lower mother-child relationship quality.
Substance abuse can be a major contributing factor to child abuse. One U.S. study found that parents with documented substance abuse, most commonly alcohol, cocaine, and heroin, were much more likely to mistreat their children, and were also much more likely to reject court-ordered services and treatments. Another study found that over two thirds of cases of child maltreatment involved parents with substance abuse problems. This study specifically found relationships between alcohol and physical abuse, and between cocaine and sexual abuse.
Unemployment and financial difficulties are associated with increased rates of child abuse. In 2009 CBS News reported that child abuse in the United States had increased during the economic recession. It gave the example of a father who had never been the primary care-taker of the children. Now that the father was in that role, the children began to come in with injuries.
A 1988 study of child murders in the US found that children are 100 times more often killed by a "non-biological parent (e.g. step-parent, co-habitee or boyfriend/girlfriend of a biological parent)" than by a biological parent. An evolutionary psychology explanation for this is that using resources in order to take care of another person's biological child is likely not a good strategy for increasing reproductive success. More generally, stepchildren have a much higher risk of being abused which is sometimes referred to as the Cinderella effect.