Obsessive–compulsive disorder (OCD) is an anxiety disorder which can range from mild and manageable to being very debilitating. Obsessions are the thoughts which then compel people to do certain things to neutralise the emotion caused by the thought.
Perhaps the most well known type of OCD is a fear of contamination or causing contamination to others which leads to anxiety/guilt or disgust, which in turn is managed by excessive washing. It can take many other forms, such as a fear of inadvertently causing harm to others, but the pattern tends to be similar in that the thought causes anxiety which is then managed by the person through a behaviour which “puts things right” in order to alleviate the distressing feeling. Over time this behaviour becomes less effective, so the person needs to do more of these behaviours and the behaviours can become elaborate and complex.
A common feature of OCD is intrusive thoughts. If these intrusive thoughts were about something inoffensive to the person they would not matter, but they are always about exactly the thing which the person is most fearful of, whatever that might be. This causes the person to take the thought seriously which leads to anxiety and neutralising behaviours or avoidance. Often people who experience these types of thoughts strongly believe the content of the thought and so feel a great deal of shame which prevents them from seeking help. Mental health professionals (and other people who also have similar thoughts) understand the nature of intrusive thoughts and will not be shocked by them. It is useful to remember that many people without OCD also experience intrusive thoughts but are able to dismiss them more readily as they do not take them so seriously.
If you think you might be experiencing OCD you will find more helpful information on the OCD Action website.