What Causes OCD?

There is no single known cause of obsessive-compulsive disorder (OCD), but there are plenty of theories. Researchers believe a combination of genetics, personality, brain structure, and environmental factors causes OCD.

Learn more about OCD, including signs and symptoms, causes, risk factors, theories, diagnosis, treatment, and more.

Young man with OCD engages in compulsive cleaning

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Signs and Symptoms of OCD

OCD is a mental disorder that involves persistent, unwanted obsessions, compulsions, or both.

Obsessions are intrusive, inappropriate, and unwanted thoughts or worries. These persistent thoughts are uncontrollable, leading to emotional distress and anxiety.

An obsession can be about almost anything. However, they often involve fears about contamination or loss, unwanted violent or religious (blasphemous) imagery, inappropriate sexual or aggressive impulses, or repetitive doubts and questions.

Compulsions refer to behaviors, rituals, or actions that someone feels an intense urge to repeat over and over to reduce anxiety or “neutralize” distress about a certain obsession. Examples include repetitive counting, praying, hoarding, organizing, cleaning, or checking.

According to the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), the obsessions and compulsions associated with OCD are time-consuming, cause significant distress, and interfere with daily life. 

For example, someone with OCD may consistently be late for work or school because they feel an uncontrollable urge to check that their door is locked over and over. Someone else may avoid friendships and romantic relationships because of their intrusive, unwanted thoughts about germs or possible contamination.

Causes and Risk Factors

OCD has no single known cause. However, several contributing factors can increase your risk of developing OCD. These may include genetics, brain structure, past life events, illness or infection, and comorbid conditions.


OCD is often an inherited disorder. People with a sibling, parent, or child who also has OCD are significantly likelier to have it themselves, especially if their relative developed OCD symptoms as a child. Studies suggest that specific OCD symptom clusters, such as hoarding, counting/checking, and cleaning/contamination, also tend to run in families.

It’s still unclear exactly how OCD is inherited. However, some researchers believe that various genetic mutations (changes in genes) may play a role in how OCD traits are passed down.

Brain Structure

Brain scans have consistently shown differences in brain activity, structure, and function among people with OCD. These differences suggest that problems in the way the brain relays information to the body (and vice versa), processes emotions, and controls impulses could contribute to the development of obsessions and compulsions. 

For example, people with OCD often exhibit excessive activity in the orbitofrontal cortex, anterior cingulate cortex, and basal ganglia—parts of the brain that are involved in emotions, impulsivity, reward, decision-making, cognitive function, and motor control.

A 2019 study revealed that people with OCD experienced both lowered inhibitions and abnormal levels of brain activity while processing errors, which could worsen the obsessive-compulsive cycle.

Life Events

Research suggests that stressful and/or traumatic life events may contribute to the development of OCD, especially among people who are genetically predisposed to the disorder. 

One 2020 study showed that over 61% of people with OCD experienced stressful life events before the onset of their disorder, while 34% of people with OCD had experienced significant trauma. Other studies have suggested that stress and trauma could increase the severity of OCD symptoms among people with the disorder.

Illness or Infection

In rare cases, severe OCD symptoms may suddenly appear in children ages 3 to 12 after an illness caused by a streptococcal (strep) infection. Examples may include scarlet fever and strep throat. 

This condition is referred to as pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). In addition to sudden or worsening OCD symptoms that appear alongside a streptococcal infection, the symptoms of PANDAS may include:

If you suspect that your child may have PANDAS, talk to your healthcare provider. Antibiotics may be used to treat the underlying strep infection, alongside treatment for OCD.

Comorbid Conditions

Many people with OCD have comorbid neurological and/or psychiatric conditions. Comorbid means they occur alongside OCD. Some of the most common include: 

  • Tourette syndrome (TS): Tourette syndrome is a nervous system disorder that causes repetitive tics (involuntary twitches, movements, and sounds). OCD and TS are difficult to distinguish from one another, and many people have both disorders. Estimates suggest that over a third of people with TS also have OCD.
  • Attention deficit hyperactivity disorder (ADHD): ADHD is a disorder that causes symptoms like impulsivity, fidgeting, hyperactivity, and difficulty paying attention. Studies show that nearly 12% of adults with OCD also have ADHD. Among children, comorbid ADHD and OCD are even more common. Over 25% of children with OCD have ADHD as well. 
  • Mental health conditions: Many people with OCD have at least one other mental health condition. For example, research suggests that people with OCD often also have depression. Many people with schizophrenia also have symptoms of OCD. Meanwhile, about 76% of people with OCD also have an anxiety disorder, such as generalized anxiety disorder (GAD).

Other Theories

Many healthcare providers agree that genetics and environmental factors often interact to increase the risk of OCD. Some researchers have offered alternative explanations about the cause of OCD, including:

  • Learning theory: Some research suggests that people with OCD have developed negative associations with certain kinds of stimuli over time. These negative associations may have conditioned them to have a fear response even when there is no real threat. Psychotherapy aims to help people with OCD get out of this negative cycle of thinking and behavior.
  • Behavioral theory: Certain learned behaviors in response to anxiety may play a role in developing OCD symptoms. For example, someone with OCD may adopt avoidance behaviors, such as going out of their way to avoid germs, to deal with emotional distress. Behavioral therapy can help people with OCD develop healthier coping skills.
  • Chemical imbalances: Studies indicate that people with OCD have lower than average levels of serotonin—a neurotransmitter that works to stabilize mood. This may be why antidepressants that affect the availability of serotonin in the brain, such as serotonin selective serotonin reuptake inhibitors (SSRIs), have been shown to improve OCD symptoms.

What Are Neurotransmitters?

Neurotransmitters are chemical messengers that transmit messages between the brain and body. Certain neurotransmitters, such as serotonin and dopamine, often play a key role in functions related to mental health (such as sleep, memory, mood, emotion, reward, reinforcement, and motivation).

How OCD Is Diagnosed

If you think you may have OCD, talk to your healthcare provider about getting a referral to a mental health provider. They may also perform a physical exam or refer you to a different specialist to rule out other possible conditions.

A mental health provider can diagnose you with OCD based on the criteria in the DSM-5, as well as a thorough understanding of your medical history and symptoms. Although OCD can appear at any age, it is usually diagnosed before the age of 25.

OCD is typically treated with psychotherapy, medication (especially antidepressants), or both. Around half of the people with OCD experience full remission of their symptoms after seeking treatment. Many others greatly improve their quality of life with the help of therapy and medicine.

One type of cognitive behavioral therapy (CBT), known as exposure and response prevention (EX/RP), involves exposing someone with OCD to the usual triggers for their obsessions within a controlled therapeutic setting while preventing them from engaging in their compulsions. EX/RP has been shown to be particularly effective in reducing the symptoms of OCD.


Obsessive-compulsive disorder (OCD) is a mental disorder that involves unwanted, time-consuming obsessions and compulsions. Obsessions are intrusive, persistent thoughts or worries. Compulsions are rituals or actions that someone feels an urge to repeat in order to reduce emotional distress.

There is no single known cause of OCD. Some of the possible contributing factors that can increase the risk of developing OCD include genetics and family history, differences in brain structure, and stressful or traumatic life events. 

Many people with OCD also have comorbid mental health conditions, such as attention deficit hyperactivity disorder (ADHD). Some researchers believe that chemical imbalances or differences in learning and thinking patterns may increase the risk of OCD.

In rare cases, certain illnesses and infections—such as streptococcal (strep) infections—can lead to the development of OCD, especially in children.

A Word From Verywell

If your obsessions or compulsions are interfering with your daily life, talk to your healthcare provider. They can talk to you about your diagnosis and treatment options for OCD.

Frequently Asked Questions

  • Is OCD an anxiety disorder?

    OCD was previously believed to be an anxiety disorder. However, it is no longer included within that umbrella category. The Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) moved OCD to the category of “obsessive compulsive and related disorders.”

  • Does OCD show up in brain scans?

    Brain scans of people with OCD show abnormal activity in several different parts of the brain. For example, people with OCD tend to have increased activity in the orbitofrontal cortex (OFC), which is involved in emotions, rewards, and decision-making.

    Brain imaging also reveals numerous differences in how the brain and body relay messages to one another.

  • What happens if OCD goes untreated?

    Depending on its severity, untreated OCD can lead to negative physical, mental, occupational, social, and emotional consequences that may significantly impair daily functioning.

    For example, someone who has a strong fear of contamination may avoid going to work, engaging in healthy relationships, or even leaving the house due to their overwhelming anxiety about germs.

    Meanwhile, someone who compulsively washes their hands may end up with raw, bleeding, or cracked skin. Some people with OCD may attempt to self-medicate by abusing drugs or alcohol.

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By Laura Dorwart
Laura Dorwart is a health journalist with particular interests in mental health, pregnancy-related conditions, and disability rights. She has published work in VICE, SELF, The New York Times, The Guardian, The Week, HuffPost, BuzzFeed Reader, Catapult, Pacific Standard, Health.com, Insider, Forbes.com, TalkPoverty, and many other outlets.