Intrusive thoughts are unwanted and often upsetting thoughts that suddenly pop into your mind. They can be about anything, like fears, worries, or strange ideas, and they can make you feel anxious or uncomfortable. These thoughts are common for many people, but for someone with OCD, they can be very persistent and hard to ignore.

Intrusive thoughts can be caused by a variety of factors, including:

1. Stress and Anxiety: High levels of stress and anxiety can trigger intrusive thoughts as your mind reacts to overwhelming feelings.
2. Trauma: Past traumatic experiences can lead to intrusive thoughts as your brain tries to process and make sense of what happened.
3. Biological Factors: Imbalances in brain chemicals or differences in brain structure can make some people more prone to intrusive thoughts.
4. Mental Health Conditions: Conditions like OCD, PTSD, and depression are often associated with frequent intrusive thoughts.
5. Fatigue: Being overly tired can reduce your ability to manage and control your thoughts effectively, leading to more intrusive thoughts.

Understanding the cause of these thoughts can help in finding effective ways to manage and cope with them.

Stopping intrusive thoughts entirely might not be possible, but there are several strategies to help manage and reduce their impact:

1. Practice Mindfulness: Focus on the present moment without judgment. This can help you observe your thoughts without getting caught up in them.
2. Cognitive Behavioral Therapy (CBT): Working with a therapist can help you challenge and change the patterns of thinking that contribute to intrusive thoughts.
3. Exposure and Response Prevention (ERP): This type of therapy, often used for OCD, involves gradually exposing yourself to the thoughts or situations that trigger anxiety, and then resisting the urge to engage in compulsive behaviors.
4. Stress Management: Reducing stress through activities like exercise, meditation, and deep breathing can decrease the frequency and intensity of intrusive thoughts.
5. Healthy Lifestyle: Maintaining a balanced diet, getting regular exercise, and ensuring enough sleep can improve overall mental health and help manage intrusive thoughts.
6. Limit Triggers: Identify and avoid specific triggers that lead to intrusive thoughts when possible.
7. Distraction Techniques: Engage in activities that require your full attention, such as hobbies or spending time with friends, to divert your mind from intrusive thoughts.
8. Acceptance: Sometimes, simply acknowledging that these thoughts are a part of your experience without giving them too much importance can reduce their power over you.

If intrusive thoughts are significantly affecting your life, it's important to seek professional help. A mental health professional can provide personalized strategies and support.