Obsessions are uncontrollable and intrusive thoughts. The process itself is passive in the sense that the person is unable to exercise control over these intrusive thoughts. It is estimated that around 75% of thoughts involve doubts, thinking 34%, 26% fears, 17% impulses, images 7%. In terms of recurring themes around 46% involve dirt, disease, contamination or illness, 29% violence and aggression, 29% moral or religious, 27% sequencing or symmetry, 10% sex and 22% various.
Such statistics tell us that obsessions may be varied, may overlap and may vary in levels of intensity. At one end of the spectrum the person may have simple doubts such as whether they locked the door, through to curious images such as seeing flesh melt, or dangerous impulses such as jumping off a cliff edge.
A point of interest here is the fact that many obsessions relate in some way to disgust or some kind of socially unacceptable behavior. The impulse to shout out during a church service or the image of cancer rotting the organs of people, are just a couple of examples. Disgust is also a common theme in other anxiety disorders (e.g. blood or spider phobia). Many issues in the headlines also find their way into obsessions, for example, swine flu or HIV/AIDS.
Compulsions refer to actions or activities. Some of these are very overt, such as repetitive hand washing, organizing objects or hoarding, and some are covert such as doing repeated calculations in the head or forming sequences out of sometimes random objects or images. There is often a rigid sequence and sometimes timing to compulsions. Some appear entirely logical if over-actioned (washing hands for fear of contamination) and some are more bizarre, such as blinking rapidly after sitting.
Compulsions have very specific rules and have to be done properly. Usually, if the ritual is interrupted or deemed not to have been properly done, the whole thing has to start from the beginning. They can also, in certain circumstances, be dangerous. I once worked with a person who looked for numbers that added to 13. If they did the person would have to close their eyes for a count of 13 in order to neutralize the distress. Sometimes once would be sufficient but sometimes the person became caught up in a repetitive cycle of obession and compulsion. Unfortunately this same person was involved in a few car accidents when the numbers of the license plate of the vehicle in front added to 13.
An obsession therefore usually has an associated compulsion. This generally serves the function of neutralizing an obsession and therefore reduces distress.