Being abused does not necessarily cause psychological or medical illness to occur. However, being abused does make it much more likely that one or more psychological or medical illnesses will occur. Victimized people commonly develop emotional or psychological problems secondary to their abuse, including anxiety disorders and various forms of depression. They may develop substance abuse disorders. If abuse has been very severe, the victim may be traumatized, and may develop a posttraumatic stress injury such as posttraumatic stress disorder (PTSD), or acute stress disorder. If abuse has occurred from a very early age and has been substantial, a personality disorder may occur (such as borderline, narcissistic, or histrionic personality disorders or in some cases, a severe dissociative disorder such as dissociative identity disorder (commonly known as multiple personality disorder). Sexual disorders may be present. Sex may be experienced as particularly undesirable, or physically or emotionally painful. Alternatively, sexual promiscuity may be observed with the increased risk of sexually transmitted diseases and unwanted pregnancy that such behavior carries. Severe abuse can even lead the victim to contemplate suicide or carry out suicidal impulses. Abuse can result in poor self-esteem, which can lead to a lack of close and trusting relationships or to body image issues (particularly for sexual abuse victims), which in turn can result in eating disorders, which can be seen as victims' attempts at self-control in one small part of life when they otherwise feels completely out of control and vulnerable.
It is important to note that abuse alone is not sufficient to create psychological disorders. Abuse can be a very strong factor contributing to their development, however. Developing a psychological disorder, such as depression, does not mean that you were necessarily abused, and being abused does not mean you will develop depression. Abuse is a sufficient cause for depression; however, there are many other reasons why someone might become depressed.
Though it is an oversimplified and perhaps even overreaching suggestion to make, it maybe easiest to think of the cluster of problems that are typically observed in the wake of abuse as all various forms of a sort of posttrauma condition, where the trauma experienced is abuse. Posttrauma conditions such as PTSD occur in the aftermath of a significant trauma (where trauma is defined as exposure to some event that involves the threat or reality of death (either one's own or another's)). Not all abuse situations get this scary, but many are disturbing enough in one way or another to make a lasting impact on a person's mind. When posttrauma illnesses occur they are characterized by the presence of three classes of symptoms. First, the posttrauma victims typically experience vivid, unwanted and highly intrusive memories of their traumatic events. Intrusive recollections may occur during waking hours or during sleep (often in the form of vivid and repetitive nightmares re-enacting the trauma). Second, posttrauma victims make efforts to avoid exposing themselves to anything that might remind them of their trauma. Third, posttrauma victims become very anxious and jumpy after their trauma. PTSD can be a very debilitating condition.
Posttrauma victims attempts at avoidance of trauma-related things can push them towards impulsive actions that less frantic people would avoid. PTSD victims commonly abuse drugs, for instance, and this drug use is thought to begin as a means of coping with trauma. Similarly, depression and sexual acting out can be thought of as attempts to cope, however, dysfunctionally. Depression functions to blunt emotional responding, and promiscuity to give into it wholly ("if I'm damaged goods I might as well act like it"). Similarly, dissociative identity disorder and the other abuse-related personality disorders represent wide-scale alterations of victim's personalities that help them shield themselves from emotional pain.