Intrusive thoughts: what, when and why

Intrusions are thoughts or mental images that come to mind unbidden and interrupt what we were doing at the time. Wondering whether you turned off the gas when sitting at your desk is a normal intrusion as everyone experiences this from time to time and it usually doesn’t cause a lot of problems or distress. However, intrusions become problematic when they are very disruptive and/or distressing. This can be a symptom of a mental disorder. For example, someone with obsessive-compulsive disorder (OCD) can have unwanted intrusions about things that might happen if they don’t act in a certain way.