Intolerance of Uncertainty: Why OCD Craves 100% Certainty

You locked the door. You know you locked the door. You even remember the click. And
yet, three steps down the street, a small voice asks: but are you sure?

That voice isn’t really asking whether the door is locked. It’s asking for something no
one can give you: 100% certainty. Psychologists call the trouble with that gap
intolerance of uncertainty, and it is one of the core beliefs researchers link to OCD.
This article explains what it is, why OCD seems to run on it, what the research actually
shows, and how people learn to live with “maybe.”

What is intolerance of uncertainty?

Intolerance of uncertainty (IU) is the tendency to react badly to not knowing. In a 2016
review, psychologist Nicholas Carleton describes it as a lasting trait: a reduced ability
to cope with the unpleasant feeling that comes when key information is missing
(Carleton, Journal of Anxiety Disorders, 2016).

In plain English: the problem isn’t the uncertainty itself, it’s how unbearable it
feels. Everyone lives with uncertainty every day. Will the plane land safely? Did that
email send? Is my partner happy? Most people notice the question, shrug, and move on. For
someone high in IU, the open question feels like an alarm that won’t switch off until
it’s answered.

Researchers usually split IU into two parts
(Carleton et al., 2007):

• Prospective IU — a strong desire for predictability. “I need to know what’s going
  to happen.” “Unforeseen events upset me greatly.”
• Inhibitory IU — feeling frozen by not knowing. “When it’s time to act,
  uncertainty paralyzes me.”

IU was first measured with a 27-item questionnaire in worry research
(Freeston et al., 1994), later
shortened to the 12-item IUS-12, and in 2026 to an ultra-brief 6-item version
(Carleton et al., 2026).

Why intolerance of uncertainty is called OCD’s engine

In 1997, an international group of OCD researchers listed the beliefs they thought drive
the disorder. Intolerance of uncertainty made the shortlist of six, alongside inflated
responsibility, overestimation of threat, perfectionism, overimportance of thoughts, and
the need to control thoughts
(Obsessive Compulsive Cognitions Working Group, Behaviour Research and Therapy, 1997).
When the group tested its questionnaire on large samples, IU clustered tightly with
perfectionism into a single “perfectionism/certainty” factor
(OCCWG, 2005). In other words, needing
things to be certain and needing them to be perfect tend to travel together.

Here’s the loop that makes IU feel like an engine:

1. An intrusive thought opens a question. “What if I hit someone with the car?”
   “What if I don’t really love my partner?”
2. The question can’t be answered with total certainty. Nobody can prove a negative.
3. The uncertainty feels intolerable, so a compulsion steps in: checking, googling,
   asking for reassurance, mentally reviewing.
4. The compulsion buys a few minutes of relief, then the doubt comes back, often
   louder, because the brain just learned that “not knowing” is an emergency that needs
   fixing.

You can see the same pattern in our articles on
reassurance seeking and
checking OCD: the ritual promises certainty, and certainty never arrives.

What the research shows

People with OCD score higher on IU (but so do others)

A 2011 meta-analysis pooled dozens of studies and found IU was strongly linked to OCD
symptoms (average correlation around .50). But it was linked just as strongly to
depression, and slightly more to generalized anxiety
(Gentes & Ruscio, Clinical Psychology Review, 2011).
So IU isn’t unique to OCD. It’s a “transdiagnostic” trait, a shared vulnerability that
shows up across anxiety and mood problems. What makes OCD different is how it tries to
fix the uncertainty: with rituals.

Checkers feel it most

In one of the first clinical studies, Tolin and colleagues gave the IU questionnaire to 55
people with OCD and 14 people without anxiety. People with checking compulsions scored
higher on IU than both people with OCD who didn’t check and the comparison group.
Repeating rituals were linked to IU too
(Tolin et al., Journal of Anxiety Disorders, 2003).

Even mild uncertainty triggers more checking

Scientists in the Netherlands tracked people’s eye movements while they searched screens
for a target. When the target was present, the answer was obvious. When it was absent,
people had to trust that they hadn’t missed it, which creates a small dose of
uncertainty. People with OCD searched longer and looked more times in both cases, but the
gap was biggest on the “absent” screens. Anxious and non-anxious comparison groups didn’t
differ from each other
(Toffolo et al., Behavior Therapy, 2016).
It didn’t take a frightening situation: mild, everyday uncertainty was enough.

A 2026 lab study of 208 adults pointed the same way: people higher in IU reported
stronger urges to check and more distress during a checking task
(Manuel et al., Cognition & Emotion, 2026).

Different OCD themes, different flavors of IU

In a sample of 974 people in intensive OCD treatment, general IU was linked to all four
main OCD symptom dimensions. But the “paralyzed by uncertainty” (inhibitory) side was
especially tied to contamination fears and to unacceptable taboo thoughts, such as
intrusive harm, sexual, or religious thoughts
(Pinciotti et al., Journal of Anxiety Disorders, 2021).

It makes decisions harder

When researchers gave people with OCD a game where they could win money by pumping up a
virtual balloon (but lose it if the balloon popped), those higher in IU took fewer risks
(Jacoby et al., Journal of Obsessive-Compulsive and Related Disorders, 2025).
And in a pre-registered 2026 experiment with 154 people diagnosed with OCD or anxiety
disorders, nudging IU up or down shifted how uncertain people felt, which in turn was
linked to more indecision about real personal choices. The effects were small and
indirect, the authors note
(Appel et al., Journal of Clinical Psychology, 2026).

The honest summary: a 2023 review concluded that IU is a likely “cognitive
vulnerability” for OCD, but more research is needed to prove that becoming more tolerant
of uncertainty is how treatment works
(Knowles & Olatunji, 2023).

How intolerance of uncertainty shows up in everyday OCD

IU rarely announces itself. It hides inside reasonable-sounding demands:

• Checking: “I’ll just check once more so I can be sure the stove is off.”
• Relationship OCD: “I need to know for certain this is the right person before I
  can relax.” (Try our relationship OCD test if this sounds
  familiar.)
• Harm thoughts: “How can I be 100% sure I’d never act on it?” See
  fear of acting on intrusive thoughts.
• Contamination: “I can’t prove my hands are clean enough, so I’ll wash again.”
• Real-event OCD: “I need to remember exactly what happened that night.”
• Health worries: hours of symptom searching to rule something out completely.

Notice the words: sure, certain, 100%, exactly, completely. OCD rarely asks “is this
likely?” It asks “can you prove it’s impossible?” That’s a test no one passes.

IU also teams up with other OCD beliefs. If a thought feels as bad as an action
(thought-action fusion) and anything bad would be your fault
(inflated responsibility), then not knowing for sure
starts to feel unbearable.

Can intolerance of uncertainty be treated?

Yes, and the good news is that the standard OCD treatments already target it.

Exposure and response prevention (ERP) is the first-line psychological treatment for
OCD in guidelines such as NICE CG31. In ERP,
you approach the doubt on purpose and then don’t do the ritual that would close the
question. Every successful exposure is a small lesson: I didn’t get certainty, and I
coped anyway. (Our complete guide to ERP therapy
explains how it works step by step.)

A 2026 study of 59 people in group CBT for OCD found that IU and OCD symptoms dropped
together over treatment. Bigger drops in the “need for predictability” side of IU went
along with bigger drops in compulsions, although the design can’t prove which caused
which (Laposa & Puccinelli, Journal of Clinical Psychology, 2026).

Modern ERP research also suggests that the goal isn’t to feel calm and certain by the end
of an exposure, but to learn that you can tolerate the feeling and that the feared outcome
is less likely than OCD predicts
(Craske et al., Behaviour Research and Therapy, 2014).
That’s practice in tolerating uncertainty by another name.

Acceptance and commitment therapy (ACT) takes a related angle: instead of trying to
win the argument with doubt, you make room for it and act on your values. See
ACT therapy for OCD.

4 ways to start building tolerance for “maybe”

These are small, everyday practices. They aren’t a replacement for therapy, but they
follow the same logic as ERP. If they feel overwhelming, a trained clinician can help you
pace them.

1. Answer doubt with “maybe.” When OCD asks “what if you left the door unlocked?”,
   try “Maybe I did, maybe I didn’t” and keep walking. You’re not trying to feel sure.
   You’re practising not needing to.
2. Delay the check. Can’t skip the ritual yet? Put 10 minutes between the urge and
   the check. Then try 20. Each delay is a small, deliberate practice in not knowing.
3. Practise low-stakes uncertainty. Order a dish you’ve never tried. Send a message
   without rereading it. Take a new route without checking the map. These build the
   “uncertainty muscle” on easier ground first.
4. Notice the certainty words. When you catch yourself thinking sure, definitely,
   100%, label it: “That’s the certainty demand again.” Naming it creates a little
   distance. Our ERP exercises for home give more structured ideas.

Practice · exercises from the ocd.app app

Practise sitting with not knowing

Face the thought 2 min Spot the OCD thought 2 min Ride the wave 1 min

Exposure and response prevention (ERP) means facing the thoughts OCD makes you avoid, without doing the ritual. Pick a thought from the app that makes you uneasy, then stay with it.

• I need absolute certainty
• Uncertainty is unmanageable
• I can't face uncertainty
• Without control - I'm useless
• Uncertainty is overpowering
• There is no joy without control
• I want to always be certain
• I must always be certain
• I have to know everything
• I must have absolute control

Educational practice, not therapy or a diagnosis. More exercises from the app · Practise daily in the ocd.app app →

If you’d like a structured way to keep practising, the ocd.app app has short daily
CBT-based exercises built around the same skill: noticing the doubt, dropping the
ritual, and moving on without an answer.

Frequently asked questions

What is intolerance of uncertainty in OCD? It’s a strong negative reaction to not
knowing for sure. In OCD, it shows up as an urge to check, ask, or review until you feel
certain, even when certainty isn’t possible
(Tolin et al., 2003).

Is intolerance of uncertainty only found in OCD? No. A meta-analysis found it’s
linked to OCD, generalized anxiety and depression at similar levels, so it’s considered
a shared vulnerability
(Gentes & Ruscio, 2011).

How is intolerance of uncertainty measured? Most often with the 12-item Intolerance
of Uncertainty Scale (IUS-12), and since 2026 also a 6-item short form
(Carleton et al., 2007;
Carleton et al., 2026). Only a
clinician can diagnose OCD.

Does therapy reduce intolerance of uncertainty? Studies suggest it does. In a 2026
group CBT study, IU and OCD symptoms fell together, though it’s not yet proven that the
drop in IU causes the improvement
(Laposa & Puccinelli, 2026;
Knowles & Olatunji, 2023).

Why does reassurance make uncertainty worse? Reassurance gives quick relief, but it
teaches your brain that doubt is an emergency that must be fixed, so the next doubt
feels just as urgent. ERP works the other way: you drop the safety behaviour and let the
question stay open, so you learn you can cope without an answer
(Craske et al., 2014).

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This article is for educational purposes and is not a substitute for professional
diagnosis or treatment. If you’re in crisis, contact your local emergency services or
a crisis line (in the US, call or text 988; in the UK, call Samaritans on 116 123).