Causes of OCD

Obsessive-Compulsive Disorder (OCD) is a mental health condition. It is characterized by obsessions: unwanted, intrusive thoughts, images or urges that cause distress. It also involves compulsions: repetitive behaviors or mental acts performed to reduce the anxiety the obsessions cause.

The Obsessive Compulsive Cognitions Working Group (OCCWG; Steketee et al., 2003) identified six key types of appraisals and beliefs. These play a crucial role in the development and maintenance of OCD.

These factors can interact with each other and with other biological, psychological, and environmental influences to contribute to the development and maintenance of OCD symptoms.

Understanding these underlying causes can help inform treatment approaches and support individuals in managing their symptoms.

1. Inflated Responsibility

People with OCD often have an overvalued sense of responsibility for preventing harm to themselves or others. They may believe that failing to prevent harm is morally equivalent to causing harm directly.

This belief can fuel excessive guilt. It creates an overwhelming need to act, even when harm is unlikely or the person has little power to prevent it.

People with inflated responsibility may worry that their actions or inactions could lead to harm, such as a fire, burglary, or injury to others.

They may repeat checking behaviors to prevent these perceived negative outcomes, such as ensuring that appliances are turned off, doors are locked, or loved ones are safe.

Paul Salkovskis developed the inflated-responsibility theory. The Oxford clinical psychologist argues that OCD is a disorder of over-conscientiousness. In a public University of Oxford webinar, he framed people with OCD as “too careful, too nice, and trying too hard” (Salkovskis, 2022).

The thoughts themselves are not the problem. On his account, they are normal and near-universal. What matters is the exaggerated responsibility that leads someone to treat a thought as a warning to act on.

2. Overimportance of Thoughts

Individuals with OCD tend to overestimate the importance and meaning of their intrusive thoughts.

They may believe that having a thought makes the event more likely to happen (thought-action fusion). They may also believe that having a morally repugnant thought is as bad as committing a morally repugnant deed (moral thought-action fusion).

These beliefs can cause significant distress. They lead to attempts to suppress or neutralize the thoughts through compulsions.

Compulsions

Compulsions, which can be observable actions or mental rituals, are performed by individuals with OCD to neutralize obsessive thoughts and alleviate distress. These compulsions are often carried out in a rigid or ritualized manner.

Compulsions may bring short-term relief. In the long run, however, they maintain OCD symptoms. They stop the person learning that their fears are unfounded and that they can tolerate the distress without compulsive behaviors.

Avoidance

People with OCD often try to avoid things that might trigger their obsessive thoughts. They do this for a few reasons:

1. To stop the obsessive thoughts from happening in the first place
2. To prevent something bad from occurring
3. To feel less distressed when they can’t completely avoid the things they fear

For example, someone with OCD might avoid certain places, such as hospitals or public bathrooms. They might avoid objects (like knives) or situations (like being alone with a child). Some avoid people, too, such as those who are sick.

If they can’t avoid these things entirely, they might try to avoid direct contact, like wearing gloves or using their sleeve to open a door.

Some people stay silent about their thoughts. This is common when the obsessions are disturbing, such as fears of harming others. They worry that revealing the thoughts could make them happen, or they feel ashamed and scared of the consequences (like having their child taken away).

Another way people avoid obsessive thoughts is by pushing them out of their mind. But they keep seeing the thoughts as dangerous. As a result, more and more things in their environment can start to trigger them.

This means they have to avoid more things. Their lives can become seriously disrupted.

While it’s understandable that people want to avoid things that make them anxious, avoiding doesn’t help in the long run.

It stops them from learning that their fears won’t necessarily come true and that they can handle the distress. Avoidance also takes up a lot of time and energy, making OCD an even bigger problem in their lives.

3. Mental Control of Thoughts

People with OCD often overvalue the importance of exerting complete control over their intrusive thoughts, images, or impulses.

They may believe that complete mental control is both possible and desirable and that any failure to control their thoughts is a sign of weakness or moral failing.

This can lead to excessive attempts to monitor and control their thoughts, paradoxically increasing the frequency and intensity of the intrusive thoughts.

Thought Suppression

People with OCD often try to push away or ignore their obsessive thoughts. They do this for a few main reasons:

1. They don’t want the thoughts to get so bad that they feel they have to perform compulsions, such as checking or making items symmetrical.
2. They want to stop their anxiety from getting worse.
3. They’re afraid the thoughts might lead to something bad happening.

Researchers think that trying not to think about something actually makes you think about it more. It’s called the “white bear effect” – if I tell you “don’t think about a white bear,” it’s hard not to picture one.

Studies of OCD tell a different story. They don’t really show that pushing away thoughts makes them happen more often.

In the study by Purdon, they found that around 30-50% of the time, ignoring obsessive thoughts actually helped people feel better and focus on other things.

Fully getting rid of obsessive thoughts does not always work. But it is not necessarily true that trying always backfires and makes the thoughts more frequent or intense.

The effects can vary from person to person and situation to situation.

4. Overestimation of Threat

Individuals with OCD tend to overestimate the severity and likelihood of negative events occurring.

They may believe that the world is a dangerous place and that bad things are more likely to happen to them than others.

This heightened perception of threat can fuel anxiety and drive compulsive behaviors aimed at reducing the perceived risk.

Hypervigilance

People with OCD often overestimate the likelihood and severity of potential threats. This leads to hypervigilance, a heightened state of alertness and sensitivity to triggers related to their obsessive concerns. This hypervigilance can manifest in several ways:

1. Monitoring for triggers: Individuals with OCD may constantly scan their environment for triggers that could provoke their obsessive thoughts, ironically even when trying to avoid these triggers.
2. Vigilance for harm: They may be on high alert for any information suggesting that harm has occurred or will occur, as well as signs that their compulsions have not successfully prevented harm.
3. Attention to internal and external cues: Hypervigilance can involve monitoring both internal (e.g., bodily sensations, thoughts) and external (e.g., environmental) information.
4. Specific manifestations: The focus of hypervigilance varies depending on the type of OCD. For example, those with contamination concerns may track “contaminated” objects, while those with repugnant obsessions may monitor their body sensations or thoughts for signs of arousal or recurrence of the obsession.

Hypervigilance is understandable. But it is ultimately unhelpful because it ensures that even minor threat indications are noticed, possibly at the expense of important safety information.

Monitoring bodily sensations can lead to misattribution of normal physiological changes. Trying to prove that harm has not occurred is futile, because the absence of evidence is not evidence of absence.

Constant self-monitoring can erode confidence in one’s senses.

Hypervigilance and avoidance are important markers of OCD severity and treatment progress, even though they are not always included in symptom measures.

5. Intolerance of Uncertainty

People with OCD often have difficulty tolerating uncertainty and may believe that they must be absolutely sure of something to avoid making mistakes.

They feel a strong need to consider all possible outcomes of a situation, leading to excessive doubting, checking, and seeking reassurance.

The inability to tolerate uncertainty sustains the obsession-compulsion cycle.

When faced with unpredictable situations or unknown future outcomes, individuals with OCD may react with heightened anxiety. They often respond by overthinking, a process of repetitive, unrealistic worry.

Overthinking takes many forms. It might include worrying about a future event or replaying a past scenario. It might also mean imagining every worst-case scenario, predicting how something will play out, or planning something to every last detail.

Compulsive rituals, avoidance behaviors, and safety behaviors in OCD can be understood as ways for individuals to seek certainty when faced with uncertainty.

David Adam lived with OCD for two decades. The science writer describes a contamination obsession, built around a terror of contracting HIV/AIDS, in his memoir The Man Who Couldn’t Stop (Adam, 2014).

A single doubt could seize him. It drove him to check his body, seek reassurance and avoid anything linked to the fear.

Adam’s central argument is that intrusive thoughts are universal. What marks out OCD, he argues, is the inability to dismiss them. His own recovery came from confronting the fear and accepting uncertainty, rather than chasing the certainty the obsession demanded.

This is one person’s account, not evidence about OCD in general.

6. Perfectionism

Individuals with OCD may believe that there is a perfect solution to problems and that even minor errors will have serious consequences.

They may tend to believe that they must be perfect at everything to be a worthwhile person.

This perfectionism can drive compulsive behaviors aimed at ensuring that tasks are completed flawlessly and can contribute to a fear of making mistakes or being judged negatively by others.

Biological and Environmental Causes of OCD

The six beliefs above describe how people interpret intrusive thoughts. Other causes work alongside them.

The most defensible picture is a diathesis-stress one. An inherited vulnerability is expressed through how a person interprets and learns from experience, and stress often triggers it.

Genetic Risk Factors

OCD runs in families. First-degree relatives are at markedly higher risk. Twin and family studies suggest genes explain roughly 40-50% of the variation in who develops OCD (Hettema et al., 2001).

There is no single OCD gene. The largest genetic study so far compared 53,660 people with OCD against more than two million controls (Strom et al., 2025).

It found 30 genome-wide significant locations. About 11,500 variants account for 90% of the heritability, and each carries only a tiny risk.

The genetic signal was concentrated in excitatory neurons of the hippocampus and cortex and in dopamine-receptor-bearing neurons of the striatum. OCD also shares genetic risk with anxiety, depression, anorexia nervosa and Tourette syndrome.

Most participants were of European ancestry. The findings may not generalize to everyone.

Brain Circuits and Serotonin

Brain imaging links OCD to a loop connecting the orbitofrontal cortex, the caudate nucleus and the thalamus.

The orbitofrontal cortex flags when something is wrong. The caudate normally helps suppress that signal.

If the loop over-activates, the alarm keeps sounding. The person checks, washes or performs other rituals to switch it off. Activity in this circuit tends to normalize after successful drug treatment or psychological therapy.

A worldwide analysis of brain scans from 1,830 people with OCD and 1,759 controls found reproducible volume differences in subcortical structures of this circuit (Boedhoe et al., 2017). The pattern differed between children and adults.

These findings are correlational. Scans cannot show whether the differences cause OCD or result from years of ritualizing.

Serotonin matters too, because drugs that raise it relieve OCD. Relief does not prove that low serotonin causes the disorder, however. Aspirin relieves a headache, but a lack of aspirin did not cause it.

Learning and Conditioning

Behavioral theories explain how OCD is maintained through learning. Mowrer’s two-process theory has two steps.

First, a neutral stimulus such as a doorknob becomes linked with anxiety through classical conditioning.

Second, the person discovers that a ritual reduces the anxiety. Operant conditioning then strengthens the ritual through negative reinforcement. Removing an unpleasant state rewards the behavior that removed it (Rachman & Hodgson, 1980).

Avoidance works the same way. It spares the anxiety but stops the fear from ever fading.

The theory is weaker on how compulsions first arise. One idea is that a behavior performed by chance just before anxiety eases is accidentally reinforced and repeated.

Skinner (1948) showed something similar. Pigeons fed at fixed intervals developed repetitive rituals.

A 2025 meta-analysis of 66 studies compared associative learning in people with OCD and controls (Myles et al., 2025). It found no reliable difference in learning in general.

The one reliable difference was a modest deficit in extinction, the unlearning of a feared association. This helps explain why compulsions persist, and why exposure and response prevention works.

The evidence was low in certainty. It is not yet clear that the deficit is specific to OCD.

Stressful Life Events

Stressful events can trigger OCD symptoms. That does not make them the root cause.

In one clinic sample of 329 patients, 60.8% had experienced a stressful life event in the year before onset (Rosso et al., 2012).

There was no comparison group. So the figure cannot show that the events were unusual.

A study of 22,084 Swedish twins compared identical twins who differed in their experiences. Abuse and family disruption was the only event factor still linked to symptom severity (Vidal-Ribas et al., 2015). It explained only 3% of the variance.

A systematic review of 128 studies reached a similar verdict (Brander et al., 2016). No environmental risk factor had been convincingly associated with OCD. Study quality was often limited.

A life event can therefore become the content of an obsession without being its cause.

Some researchers also propose a post-traumatic subtype, in which symptoms follow a traumatic event (Fontenelle et al., 2012). See also why OCD can suddenly get worse.

References

Adam, D. (2014). The man who couldn’t stop: OCD and the true story of a life lost in thought. Picador.

Boedhoe, P. S. W., Schmaal, L., Abe, Y., Ameis, S. H., Arnold, P. D., Batistuzzo, M. C., Benedetti, F., Beucke, J. C., Bollettini, I., … van den Heuvel, O. A. (2017). Distinct subcortical volume alterations in pediatric and adult OCD: A worldwide meta- and mega-analysis. American Journal of Psychiatry, 174(1), 60-69. https://doi.org/10.1176/appi.ajp.2016.16020201

Brander, G., Pérez-Vigil, A., Larsson, H., & Mataix-Cols, D. (2016). Systematic review of environmental risk factors for obsessive-compulsive disorder: A proposed roadmap from association to causation. Neuroscience & Biobehavioral Reviews, 65, 36-62. https://doi.org/10.1016/j.neubiorev.2016.03.011

Fontenelle, L. F., Cocchi, L., Harrison, B. J., Shavitt, R. G., do Rosário, M. C., Ferrão, Y. A., de Mathis, M. A., Cordioli, A. V., Yücel, M., Pantelis, C., Mari, J. de J., Miguel, E. C., & Torres, A. R. (2012). Towards a post-traumatic subtype of obsessive-compulsive disorder. Journal of Anxiety Disorders, 26(2), 377-383. https://doi.org/10.1016/j.janxdis.2011.12.001

Hettema, J. M., Neale, M. C., & Kendler, K. S. (2001). A review and meta-analysis of the genetic epidemiology of anxiety disorders. American Journal of Psychiatry, 158(10), 1568-1578. https://doi.org/10.1176/appi.ajp.158.10.1568

Myles, L. A. M., Hotton, M., Madden, F., & Salkovskis, P. M. (2025). Systematic review and meta-analysis examining the effect of obsessive-compulsive disorder on associative learning. Clinical Psychology Review, 122, Article 102661. https://doi.org/10.1016/j.cpr.2025.102661

Rachman, S., & Hodgson, R. J. (1980). Obsessions and compulsions. Prentice-Hall.

Rosso, G., Albert, U., Asinari, G. F., Bogetto, F., & Maina, G. (2012). Stressful life events and obsessive-compulsive disorder: Clinical features and symptom dimensions. Psychiatry Research, 197(3), 259-264. https://doi.org/10.1016/j.psychres.2011.10.005

Salkovskis, P. (2022, February 18). Obsessive compulsive disorder: Too careful, too nice, and trying too hard [Webinar]. University of Oxford Podcasts. https://podcasts.ox.ac.uk/obsessive-compulsive-disorder-too-careful-too-nice-and-trying-too-hard

Skinner, B. F. (1948). “Superstition” in the pigeon. Journal of Experimental Psychology, 38(2), 168-172. https://doi.org/10.1037/h0055873

Strom, N. I., Gerring, Z. F., Galimberti, M., Yu, D., Halvorsen, M. W., Abdellaoui, A., Rodriguez-Fontenla, C., Sealock, J. M., Bigdeli, T., … Mattheisen, M. (2025). Genome-wide analyses identify 30 loci associated with obsessive-compulsive disorder. Nature Genetics, 57(6), 1389-1401. https://doi.org/10.1038/s41588-025-02189-z

Vidal-Ribas, P., Stringaris, A., Rück, C., Serlachius, E., Lichtenstein, P., & Mataix-Cols, D. (2015). Are stressful life events causally related to the severity of obsessive-compulsive symptoms? A monozygotic twin difference study. European Psychiatry, 30(2), 309-316. https://doi.org/10.1016/j.eurpsy.2014.11.008