Like an obsession, a compulsion also has an everyday meaning. It is defined in the dictionary as an irresistible impulse to act, regardless of the motivation. However, this includes all sorts of behaviors such as shoplifting, binge-eating, sex addiction, or gambling, which are done for immediate gratification, and are different from the compulsions of OCD.
Compulsions in OCD
In OCD, compulsions are acts that you repeat over and over again in response to an obsession. The aim of a compulsion is to reduce the liklihood of harm, so that you can feel 'just right' or 'comfortable', although over time they some times stop 'working'. A compulsion can be an act that may be observed by others(e.g. checking that a door is locked until you feel 'just right') or a mental act that cannot be observed by others(e.g. saying a certain phrase in your mind).
Mental compulsions are often complex, and may not be repeated over and over again. An example in OCD is saying a special phrase to prevent one's partner from dying. This is referred to as 'neutralizing'. Most people with OCD have more than one compulsion, but one or two predominate.
Certain compulsions tend to go with certain obsessions. For example, the most common combination is an obsession about contamination from germs or a bodily fluid that is linked with compulsive washing and cleaning. Another common combination is an obsession about causing harm leading to frequent checking (e.g. of door locks, gas taps, electrical appliances).
Compulsions like washing and checking persist because they seem to 'work' by reducing distress or preventing anxiety. However, over time compulsions do not always go on 'working'. Carrying out a compulsion may briefly reduce anxiety, but in the long term it increases the frequency of the obsesion and the urge to perform the compulsion again.
One of the main differences between compulsions and the same actions performed normally by individuals without OCD is the reasons for finishing a compulsion. Someone without OCD finishes washing their hands when they can see that their hands are clean. However, someone with an obsessive fear of contamination finishes not when they can see that their hands are clean, but only when they feel 'comfortable' or 'just right'
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