What causes OCD?

There are different theories about why someone develops OCD. No theory can fully explain every person's experience.

But research suggests that it may be to do with personal experiences, and biological factors. This page explains more about these factors.

Mae'r dudalen hon hefyd ar gael yn Gymraeg. This link will take you to a Welsh translation of this page.

On this page:

Even though we don't fully understand what causes OCD, it can still be successfully treated. See our page on OCD treatment for more information.

Personal experiences and OCD

Some theories suggest that OCD is caused by personal experience. For example:

If you've had a painful childhood experience, or suffered trauma, abuse, discrimination or bullying, you might learn to use obsessions and compulsions to cope with anxiety.
If your parents had similar anxieties and showed similar kinds of compulsive behaviour, you may have learned OCD behaviours as a coping technique.
Ongoing anxiety or stress could trigger OCD or make it harder to manage.
Pregnancy or giving birth can sometimes trigger perinatal OCD. Read more about perinatal OCD.

Biological factors and OCD

Some theories suggest that OCD may be caused by something physical in our body or brain. These are sometimes called biological factors.

Some biological theories suggest that a lack of the brain chemical serotonin may have a role in OCD. However, it's unclear whether this is a cause or an effect of the condition.

Studies have also looked at genetic factors and how different parts of the brain might be involved in causing OCD. But they haven't found anything definite.

You can read more about the causes of OCD on the OCD-UK website.

Is childhood OCD caused by an infection?

Some experts have noted that some children seem to develop OCD symptoms very suddenly after having a streptococcal (or strep) infection. For example, strep throat or scarlet fever.

This is sometimes referred to as PANS (Paediatric Acute-onset Neuropsychiatric Syndrome) or PANDAS (Paediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcus).

More research is needed into why this can happen and the best options for treatment.

You can find more information and support from the charity PANS PANDAS UK.

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This information was published in October 2023. We will revise it in 2026.

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