The prevalence of scrupulosity is speculative. Available data do not permit reliable estimates, and available analyses mostly disregard associations with age or with gender, and have not reliably addressed associations with geography or ethnicity. Available data suggest that the prevalence of obsessive–compulsive disorder does not differ by culture, except where prevalence rates differ for all psychiatric disorders. No association between OCD and depth of religious beliefs has been demonstrated, although data are scarce. There are large regional differences in the percentage of OCD patients who have religious obsessions or compulsions, ranging from 0–7% in countries like the U.K. and Singapore, to 40–60% in traditional Muslim and orthodox Jewish populations.

Socioeconomic status has also been looked at as a potential cause for personality disorders. There is a strong association with low parental/neighborhood socioeconomic status and personality disorder symptoms. In a recent study comparing parental socioeconomic status and a child's personality, it was seen that children who were from higher socioeconomic backgrounds were more altuistic, less risk seeking, and had overall higher IQs. These traits correlate with a low risk of developing personality disorders later on in life. In a study looking at female children who were detained for disciplinary actions found that psychological problems were most negatively associated with socioeconomic problems. Furthermore, social disorganization was found to be inversely correlated with personality disorder symptoms.

Child abuse and neglect consistently show up as risk factors to the development of personality disorders in adulthood. A study looked at retrospective reports of abuse of participants that had demonstrated psychopathology throughout their life and were later found to have past experience with abuse. In a study of 793 mothers and children, researchers asked mothers if they had screamed at their children, and told them that they did not love them or threatened to send them away. Children who had experienced such verbal abuse were three times as likely as other children (who did not experience such verbal abuse) to have borderline, narcissistic, obsessive-compulsive or paranoid personality disorders in adulthood. The sexually abused group demonstrated the most consistently elevated patterns of psychopathology. Officially verified physical abuse showed an extremely strong correlation with the development of antisocial and impulsive behavior. On the other hand, cases of abuse of the neglectful type that created childhood pathology were found to be subject to partial remission in adulthood.

The cause of OCPD is unknown. However, it is believed to involve a combination of genetic and environmental factors. Under the genetic theory, people with a form of the DRD3 gene will probably develop OCPD and depression, particularly if they are male. But genetic concomitants may lie dormant until triggered by events in the lives of those who are predisposed to OCPD. These events could include trauma faced during childhood, such as physical, emotional, or sexual abuse, or other psychological trauma. Under the environmental theory, OCPD is a learned behavior.

A 2007 study found that 78% of a clinical sample of OCD patients had intrusive images. Most people who suffer from intrusive thoughts have not identified themselves as having OCD, because they may not have what they believe to be classic symptoms of OCD, such as handwashing. Yet, epidemiological studies suggest that intrusive thoughts are the most common kind of OCD worldwide; if people in the United States with intrusive thoughts gathered, they would form the fourth-largest city in the US, following New York City, Los Angeles, and Chicago.

The prevalence of OCD in every culture studied is at least 2% of the population, and the majority of those have obsessions, or bad thoughts, only; this results in a conservative estimate of more than 2 million sufferers in the United States alone (as of 2000). One author estimates that one in 50 adults have OCD and about 10–20% of these have sexual obsessions. A recent study found that 25% of 293 patients with a primary diagnosis of OCD had a history of sexual obsessions.

Primarily cognitive obsessive-compulsive disorder (also commonly called "primarily obsessional OCD", purely obsessional OCD, Pure-O, OCD without overt compulsions or with covert compulsions) is a lesser-known form or manifestation of OCD. For people with primarily obsessional OCD, there are fewer observable compulsions, compared to those commonly seen with the typical form of OCD (checking, counting, hand-washing, etc.). While ritualizing and neutralizing behaviors do take place, they are mostly cognitive in nature, involving mental avoidance and excessiverumination. Primarily obsessional OCD often takes the form of intrusive thoughts of a distressing or violent nature.

Obsessive love is a condition in which one person feels an overwhelming obsessive desire to possess and protect another person toward whom one feels a strong attraction, with an inability to accept failure or rejection. Although not categorized specifically under any specific mental diagnosis by the DSM-5, some people argue that obsessive love is considered to be a mental illness similar to attachment disorder, borderline personality disorder, and erotomania. Depending on the intensity of their attraction, obsessive lovers may feel entirely unable to restrain themselves from extreme behaviors such as acts of violence toward themselves or others. Obsessive love can have its roots in childhood trauma, and may begin at first sight; it may persist indefinitely, sometimes requiring psychotherapy.

Obsessive love occurs in both women and men, making it a gender neutral phenomenon.

In psychology, relationship obsessive–compulsive disorder (ROCD) is a form of obsessive-compulsive disorder focusing on intimate relationships (whether romantic or non-romantic). Such obsessions can become extremely distressing and debilitating, having negative impacts on relationships functioning.

Like other forms of OCD, psychological and biological factors are believed to play a role in the development and maintenance of ROCD. In addition to the maladaptive ways of thinking and behaving identified as important in OCD, models of ROCD suggest that over-reliance on intimate-relationships or the perceived value of the partner for a person's feelings of self-worth and fear of abandonment (also see attachment theory) may increase vulnerability and maintain ROCD symptoms.

Sexual obsessions are obsessions with sexual activity. In the context of obsessive-compulsive disorder (OCD), these are extremely common, and can become extremely debilitating, making the person ashamed of the symptoms and reluctant to seek help. As preoccupation with sexual matters, however, does not only occur as a symptom of OCD, they may be enjoyable in other contexts (i.e. sexual fantasy).

In scrupulosity, a person's obsessions focus on moral or religious fears, such as the fear of being an evil person or the fear of divine retribution for sin. Although it can affect nonreligious people, it is usually related to religious beliefs. In the strict sense, not all obsessive–compulsive behaviors related to religion are instances of scrupulosity: strictly speaking, for example, scrupulosity is not present in people who repeat religious requirements merely to be sure that they were done properly.

Estimates for the prevalence of OCPD in the general population range from 2.1% to 7.9%. A large U.S. study found a prevalence rate of 7.9%, making it the most common personality disorder. Men are diagnosed with OCPD about twice as often as women. It may occur in 8–9% of psychiatric outpatients.

Some evidence based on brain lesion case studies also suggests that the anterior ventromedial prefrontal and cingulate cortices may be involved in abnormal hoarding behaviors, but sufferers of such injuries display less purposeful behavior than other individuals who hoard compulsively, thus making the involvement of these brain structures unclear. Other neuropsychological factors that have been found to be associated with individuals exhibiting hoarding behaviors include slower and more variable reaction times, increased impulsivity, and decreased spatial attention. A study comparing neural activity in hoarders, people with OCD, and a control group when deciding to throw possessions away found that when hoarders were trying to decide to throw away their own possessions, they had lower activity in the anterior cingulate cortex and insula regions of the brain. The study suggested this lower activity was related to "problems in identifying the emotional significance of a stimulus, generating appropriate emotional response, or regulating affective state during decision making." Hoarders had normal levels of activity in those regions when making decisions about possessions that did not belong to them.

Perfectionism, in psychology, is a personality trait characterized by a person's striving for flawlessness and setting high performance standards, accompanied by critical self-evaluations and concerns regarding others' evaluations. It is best conceptualized as a multidimensional characteristic, as psychologists agree that there are many positive and negative aspects. In its maladaptive form, perfectionism drives people to attempt to achieve an unattainable ideal, while their adaptive perfectionism can sometimes motivate them to reach their goals. In the end, they derive pleasure from doing so. When perfectionists do not reach their goals, they often fall into depression.

An intrusive thought is an unwelcome involuntary thought, image, or unpleasant idea that may become an obsession, is upsetting or distressing, and can feel difficult to manage or eliminate. When such thoughts are associated with obsessive-compulsive disorder (OCD), depression, body dysmorphic disorder (BDD), and sometimes attention-deficit hyperactivity disorder (ADHD), the thoughts may become paralyzing, anxiety-provoking, or persistent. Intrusive thoughts may also be associated with episodic memory, unwanted worries or memories from OCD, posttraumatic stress disorder, other anxiety disorders, eating disorders, or psychosis. Intrusive thoughts, urges, and images are of inappropriate things at inappropriate times, and generally have aggressive, sexual, or blasphemous themes.

Not only are there significant health risks associated with compulsive hoarding, but scientists are also trying to pinpoint how significant the interference is with occupational and social functioning in a hoarder's daily life. In a pool of compulsive hoarders, 42% found their behavior problematic to the 63% of their family and friends who saw the behavior as problematic. The findings suggest that individuals who hoard may exhibit impaired sensitivity to their own and others’ emotions, and conversely, relate the world around them by forming attachments to possessions rather than to people. Lower emotional intelligence among hoarding patients may also impact their ability to discard and organize their possessions. With such detrimental characteristics, comprehensive research has been performed to find a cure. Although this is ongoing research, most investigations have found that only a third of patients who hoard show an adequate response to these medications and therapeutic interventions.

With the modifications to the DSM, insurance coverage for treatments will change as well as special education programs.

Egomania is also known as an obsessive preoccupation with one's self and applies to someone who follows their own ungoverned impulses and is possessed by delusions of personal greatness and feels a lack of appreciation. Someone suffering from this extreme egocentric focus is an egomaniac. The condition is psychologically abnormal.

The term "egomania" is often used by laypersons in a pejorative fashion to describe an individual who is intolerably self-centred. The clinical condition that most resembles the popular conception of egomania is narcissistic personality disorder.

Perfectionists strain compulsively and unceasingly toward unobtainable goals, and measure their self-worth by productivity and accomplishment. Pressuring oneself to achieve unrealistic goals inevitably sets the person up for disappointment. Perfectionists tend to be harsh critics of themselves when they fail to meet their standards.

Many people with sexual obsessions are alarmed that they seem to lose their sex drive. People with OCD may see this as evidence that they no longer have normal sexual attractions and are in fact deviant in some way. Some may wonder if medication is the answer to the problem. Medication is a double-edged sword. Drugs specifically for erectile dysfunction (i.e. Viagra, Cialis) are not the answer for people with untreated OCD. The sexual organs are working properly, but it is the anxiety disorder that interferes with normal libido.

Medications specifically for OCD (typically SSRI medications) will help alleviate the anxiety but will also cause some sexual dysfunction in about a third of patients. For many the relief from the anxiety is enough to overcome the sexual problems caused by the medication. For others, the medication itself makes sex truly impossible. This may be a temporary problem, but if it persists a competent psychiatrist can often adjust the medications to overcome this side-effect.

Compulsive decluttering is a pattern of behavior that is characterized by an excessive desire to discard objects in one's home and living areas. Other terms for such behavior includes obsessive compulsive spartanism. The homes of compulsive declutterers are often empty. It is the antonym of compulsive hoarding.

Quality of life is reduced across all domains in OCD. While psychological or pharmacological treatment can lead to a reduction of OCD symptoms and an increase in QoL, symptoms may persist at moderate levels even following adequate treatment courses, and completely symptom-free periods are uncommon. In pediatric OCD, around 40% still have the disorder in adulthood, and around 40% qualify for remission.

As with most mental disorders, BDD's causation is likely intricate, altogether biopsychosocial, through an interaction of multiple factors, including genetic, developmental, psychological, social, and cultural. BDD usually develops during early adolescence, although many patients note earlier trauma, abuse, neglect, teasing, or bullying. Though twin studies on BDD are few, one estimated its heritability at 43%. Yet BDD's causation may also involve introversion, negative body image, perfectionism, heightened aesthetic sensitivity, and childhood abuse and neglect. Media influence has also been identified as a factor causing poor body image.

The core symptom of the disorder is that the sufferer holds an unshakable belief that another person is secretly in love with them. In some cases, the sufferer may believe several people at once are "secret admirers". The sufferer may also experience other types of delusions concurrently with erotomania, such as delusions of reference, wherein the perceived admirer secretly communicates his or her love by subtle methods such as body posture, arrangement of household objects, and other seemingly innocuous acts (or, if the person is a public figure, through clues in the media). Erotomanic delusions are typically found as the primary symptom of a delusional disorder or in the context of schizophrenia and may be treated with atypical antipsychotics.

Erotomania is a type of delusional disorder where the affected person believes that another person is in love with him or her. This belief is usually applied to someone with higher status or a famous person, but can also be applied to a complete stranger. Erotomanic delusions often occur in patients with schizophrenia and other psychotic disorders, but can also occur during a manic episode in the context of bipolar I disorder. During an erotomanic delusion, the patient believes that a secret admirer is declaring his or her affection for the patient, often by special glances, signals, telepathy, or messages through the media. Usually the patient then returns the perceived affection by means of letters, phone calls, gifts, and visits to the unwitting recipient. Even though these advances are unexpected and often unwanted, any denial of affection by the object of this delusional love is dismissed by the patient as a ploy to conceal the forbidden love from the rest of the world.

Erotomania is also called de Clérambault's syndrome, after French psychiatrist Gaëtan Gatian de Clérambault (1872–1934), who published a comprehensive review paper on the subject ("Les Psychoses Passionnelles") in 1921. Erotomania should not be confused with obsessive love or obsession with unrequited love, neither of which involves delusion.

Those suffering from primarily obsessional OCD might appear normal and high-functioning, yet spend a great deal of time ruminating, trying to solve or answer any of the questions that cause them distress. Very often, Pure O sufferers are dealing with considerable guilt and anxiety. Ruminations may include trying to think about something 'in the right way' in an attempt to relieve this distress.

For example, an intrusive thought "I could just kill Bill with this steak knife" is followed by a catastrophic misinterpretation of the thought, i.e. "How could I have such a thought? Deep down, I must be a psychopath." This might lead a person to continually surf the Internet, reading numerous articles on defining psychopathy. This reassurance-seeking ritual will, ironically, provide no further clarification and could exacerbate the intensity of the search for the answer. There are numerous corresponding cognitive biases present, including thought-action fusion, over-importance of thoughts, and need for control over thoughts.

Despite how real and imposing the intrusive thoughts may be to an individual, the sufferer will probably never carry out actions related to these thoughts, even if one believes themselves capable of doing so. One of the reasons for this is because the person in question will go to extreme lengths to avoid circumstances which could trigger their intrusive thoughts.

The disorder is particularly easy to miss by many well-trained clinicians, as it closely resembles markers of generalized anxiety disorder and does not include observable, compulsive behaviors. Clinical "success" is reached when the sufferer becomes indifferent to the need to answer the question. While many clinicians will mistakenly offer reassurance and try to help their patient achieve a definitive answer (an unfortunate consequence of therapists treating primarily obsessional OCD as generalized anxiety disorder), this method only contributes to the intensity or length of the patient's rumination, as the neuropathways of the OCD brain will predictably come up with creative ways to "trick" the person out of reassurance, negating any temporary relief and perpetuating the cycle of obsessing.

The most effective treatment for primarily obsessional OCD appears to be cognitive-behavioral therapy. (more specifically exposure and response prevention (ERP)) as well as cognitive therapy (CT) which may or may not be combined with the use of medication, such as SSRIs. People suffering from OCD without overt compulsions are considered by some researchers more refractory towards ERP compared to other OCD sufferers and therefore ERP can prove less successful than CT.

ERP of Pure-O is theoretically based on the principles of classical conditioning and extinction. The spike often presents itself as a paramount question or disastrous scenario. A response that answers the spike in a way that leaves ambiguity is sometimes warranted. "If I don't remember what I had for breakfast yesterday my mother will die of cancer!" Using the antidote procedure, a cognitive response would be one in which the subject accepts this possibility and is willing to take the risk of his mother dying of cancer or the question recurring for eternity. No effort is expended in directly answering the question in an effort to find resolution. In another example, the spike would be, "Maybe I said something offensive to my boss yesterday." A recommended response would be, "Maybe I did. I'll live with the possibility and take the risk he'll fire me tomorrow." Using this procedure, it is imperative that the distinction be made between the therapeutic response and rumination. The therapeutic response does not seek to answer the question but to accept the uncertainty of the unsolved dilemma.

Acceptance and commitment therapy (ACT) is a newer approach that also is used to treat purely obsessional OCD, as well as other mental disorders such as anxiety and clinical depression. Mindfulness-based stress reduction (MBSR) may also be helpful for breaking out of the ruminative thinking process.