Obsessive compulsive disorder is a type of anxiety disorder primarily characterized by obsessions and/or compulsions. Obsessions are distressing, repetitive, intrusive thoughts or images that the individual often realizes are senseless. Compulsions are repetitive behaviors that the person feels forced or compelled into doing, sometimes, in order to relieve anxiety. The OCD thought pattern may be likened to superstitions: if X is done, Y won't happen?in spite of how unlikely it may be that doing X will actually prevent Y, if Y is even a real threat to begin with. A common example of this behavior would be obsessing that one's door is unlocked, which may lead to compulsive constant checking and rechecking of doors. Another example is obsession with the state of one's personal items, such as eyeglasses, leading to their excessive cleaning or adjustment. Often the process seems much less logical. For example, the compulsion of walking in a certain pattern may be employed to alleviate the obsession that something bad is about to happen. More often, though, the compulsion is inexplicable, simply an urge to complete a ritual triggered by nervousness. Light switches and other household items are also common objects of obsession.

To be diagnosed with OCD, a person must have either obsessions or compulsions alone, or obsessions and compulsions, according to the DSM-IV-TR diagnostic criteria. The Quick Reference to the diagnostic criteria from DSM-IV-TR (2000) states several characteristics of obsessions and compulsions:

In addition to these criteria, at some point during the course of the disorder, the individual must realize that his/her obsessions or compulsions are unreasonable or excessive. Moreover, the obsessions or compulsions must be time-consuming (taking up more than one hour per day), cause distress, or cause impairment in social, occupational, or school functioning. OCD often causes feelings similar to those of depression.

OCD manifests in a variety of forms. Studies have placed the prevalence between one and three percent, although the prevalence of clinically-recognized OCD is much lower, suggesting that many individuals with the disorder may not be diagnosed. The fact that many individuals do not seek treatment may be due in part to stigma associated with OCD. Another reason for not seeking treatment is because many sufferers of OCD do not realize that they have the condition.

The typical OCD sufferer performs tasks (or compulsions) to seek relief from obsession-related anxiety. To others, these tasks may appear odd and unnecessary. But for the sufferer, such tasks can feel critically important, and must be performed in particular ways to ward off dire consequences and to stop the stress from building up. Examples of these tasks are repeatedly checking that one's parked car has been locked before leaving it, turning lights on and off a set number of times before exiting a room, repeatedly washing hands at regular intervals throughout the day, touching objects a certain amount of times before leaving a room, or walking in a certain routine way. Physical symptoms may include those brought on from anxeties and unwanted thoughts, as well as tics or Parkinson's disease-like symptoms: rigidity, tremor, jerking arm movements, or involuntary movements of the limbs.

However, the general idea of a person with OCD (washing hands, checking doors etc.) is not always the case. There are OCD sufferers who are convinced that reality is non-existent, that they are destroying people's souls merely by looking at them, that people are being possessed and many more.

There are many other possible symptoms, and it is not necessary to display those described in the lists below to be considered as suffering from OCD. Formal diagnosis should be performed by a psychologist, a psychiatrist or psychoanalyst. OCD sufferers are aware that their thoughts and behavior are not rational, but they feel bound to comply with them to fend off feelings of panic or dread. Although everyone may experience unpleasant thoughts at one time or another, these are short-lived and fade away in time.For people with OCD, the thoughts are intrusive and persistent, and cause them great anxiety and distress.

A major subtype of the fear category is the fear of contamination:(see mysophobia); some sufferers may fear the presence of human body secretions such as saliva, blood, sweat, tears, vomit, or mucus, or excretions such as urine or feces. Some OCD sufferers even fear that the soap they are using is contaminated^. As with the other anxieties, these fears may cause a person to have significant distress, and they may make it hard for a person with OCD to work or go to school or interfere with social relationships.

Symptoms related to performing tasks may include repeated hand washing or clearing of the throat; specific counting systems or counting of steps; doing repetitive actions -- more generally, this can involve an obsession with numbers or types of numbers (e.g., odd numbers). These obsessive behaviours can cause individuals to feel psychological distress, because they are very concerned about having "made mistakes" in the number of steps that they have taken, or the number of stairs on a staircase. For some people with OCD, these obsessive counting and re-counting tasks, along with the attendant anxiety and fear, can take hours of each day, which can make it hard for the person to fulfill their work, family, or social roles. In some cases, these behaviours can also cause adverse physical symptoms: people who obsessively wash their hands with antibacterial soap and hot water (to remove germs) can make their skin red and raw with dermatitis.

Intrusive thoughts are unwelcome, involuntary thoughts, images or unpleasant ideas that may become obsessions, are upsetting or distressing, and can be difficult to be free of and manage. Intrusive thoughts, urges, and images are of inappropriate things at inappropriate times, usually falling into three categories: inappropriate aggressive thoughts, inappropriate sexual thoughts, or blasphemous religious thoughts. Most people experience these thoughts; when they are associated with OCD or depression, they may become paralyzing, anxiety-provoking, and persistent. Many people experience the type of unpleasant or unwanted thoughts that people with more troubling intrusive thoughts have, but most people are able to dismiss these thoughts. When intrusive thoughts co-occur with OCD, patients are less able to ignore the unpleasant thoughts and may pay undue attention to them, causing the thoughts to become more frequent and distressing.

Intrusive thoughts may involve violent obsessions about hurting others or one's self. They can include such thoughts as harming an innocent child, jumping from a bridge, mountain or the top of a tall building, urges to jump in front of a train or automobile, and urges to push another in front of a train or automobile. A survey of healthy college students found that virtually all of them had intrusive thoughts from time to time, including imagining or wishing harm upon a family member or friend, impulses to attack or kill a small child, or animal, or shout something rude or violent. A person with OCD may meet up with their best friend, to whom they bear no ill will, and an image of them stabbing their friend may "pop" into their head.

While some individuals with OCD who have these unwanted images pop into their minds are able to dismiss the images as random "static" generated by the mind, others are tormented by the thoughts, and they may worry that they are actual desires that they may act on, or that they are "going crazy." In some cases, the person struggling with these horrible images may try to deal with them by developing compulsions. For example, a person who is tormented by unwanted thoughts of them stabbing their mother with a kitchen knife may ensure that all kitchen knives are kept locked away, to prevent the perceived danger that they may "act upon" the horrible thoughts.

The possibility that most patients suffering from intrusive thoughts will ever act on those thoughts is low; patients who are experiencing intense guilt, anxiety, shame, and upset over bad thoughts are different from those who actually act on bad thoughts. The history of violent crime is dominated by those who feel no guilt or remorse; the very fact that someone is tormented by intrusive thoughts, and has never acted on them before, is an excellent predictor that they won't act upon the thoughts. According to Baer, a patient should be concerned that intrusive thoughts are dangerous if the person doesn't feel upset by the thoughts, rather finds them pleasurable; has ever acted on violent or sexual thoughts or urges; hears voices or sees things that others don't see; or feels uncontrollable irresistible anger.

Sexual obsessions involve intrusive thoughts or images of "kissing, touching, fondling, oral sex, anal sex, intercourse, and rape" with "strangers, acquaintances, parents, children, family members, friends, coworkers, animals and religious figures", involving "heterosexual or homosexual content" with persons of any age. Like other intrusive, unpleasant thoughts or images, most people have some inappropriate sexual thoughts at times, but people with OCD may attach significance to the unwanted sexual thoughts, generating anxiety and distress. The doubt that accompanies OCD leads to uncertainty regarding whether one might act on the bad thoughts, resulting in self-criticism or loathing.

One of the more common sexual intrusive thoughts occurs when an obsessive person doubts his or her sexual identity, a symptom of OCD called homosexuality anxiety or HOCD. As in the case of most sexual obsessions, sufferers may feel shame and live in isolation, finding it hard to discuss their fears, doubts, and concerns about their sexual identity. A person experiencing sexual intrusive thoughts may feel shame, "embarrassment, guilt, distress, torment, fear that you may act on the thought or perceived impulse and, doubt about whether you have already acted in such a way." Depression may be a result of the self-loathing that can occur, depending on how much the OCD interferes with daily functioning or causes distress. The possibility that most patients suffering from intrusive thoughts to sexually assault people will ever act on those thoughts is low; patients who are experiencing intense guilt, anxiety, shame, and upset over bad thoughts are different from those who actually act on bad thoughts.

OCD is often confused with the separate condition obsessive-compulsive personality disorder. The two are not the same condition, however. OCD is ego dystonic, meaning that the disorder is incompatible with the sufferer's self-concept. Because disorders that are ego dystonic go against an individual's perception of his/herself, they tend to cause much distress. OCPD, on the other hand, is ego syntonic - marked by the individual's acceptance that the characteristics displayed as a result of this disorder are compatible with his/her self-image. Ego syntonic disorders understandably cause no distress. Persons suffering from OCD are often aware that their behavior is not rational and are unhappy about their obsessions but nevertheless feel compelled by them. Persons with OCPD are not aware of anything abnormal about themselves; they will readily explain why their actions are rational, and it is usually impossible to convince them otherwise. Persons with OCD are ridden with anxiety; persons who suffer from OCPD, by contrast, tend to derive pleasure from their obsessions or compulsions. This is a significant difference between these disorders.

Equally frequently, these rationalizations do not apply to the overall behavior, but to each instance individually; for example, a person compulsively checking their front door may argue that the time taken and stress caused by one more check of the front door is considerably less than the time and stress associated with being robbed, and thus the check is the better option. In practice, after that check, the individual is still not sure, and it is still better in terms of time and stress to do one more check, and this reasoning can continue as long as necessary.

Some OCD sufferers exhibit what is known as overvalued ideas. In such cases, the person with OCD will truly be uncertain whether the fears that cause them to perform their compulsions are irrational or not. After some discussion, it is possible to convince the individual that their fears may be unfounded. It may be more difficult to do ERP therapy on such patients, because they may be, at least initially, unwilling to cooperate. For this reason OCD has often been likened to a disease of pathological doubt, in which the sufferer, while not usually delusional, is often unable to realize fully what sorts of dreaded events are reasonably possible and which are not.

OCD is different from behaviors such as gambling addiction and overeating. People with these disorders typically experience at least some pleasure from their activity; OCD sufferers do not actively want to perform their compulsive tasks, and experience no pleasure from doing so. OCD is placed in the anxiety class of mental illness, but like many chronic stress disorders it can lead to clinical depression over time. The constant stress of the condition can cause sufferers to develop a deadening of spirit, a numbing frustration, or sense of hopelessness. OCD's effects on day-to-day life - particularly its substantial consumption of time - can produce difficulties with work, finances and relationships. There is no known cure for OCD as of yet, but there are a number of successful treatment options available.