OCD obsessions and compulsions are best illustrated with an example. A common obsession is the fear of contamination. The belief that one's hands might be dirty or contaminated, for instance, can give a sufferer a high level of fear even when there is no evidence of contamination. The fear can be so intense that they may believe that there could be a dangerous - even life threatening - consequence of the 'contamination' unless it is dealt with immediately. This obsession then leads to the compulsion of hand washing, which may continue until the sufferer 'feels clean'. In OCD this act of washing wrongly reinforces the sufferer's belief that their hands were contaminated in the first place and that the 'danger' was actually removed by the act of washing. Unfortunately, it is not long before the sufferer once again succumbs to the sense of being dirty and the OCD cycle continues.

This is a vicious circle. Contamination fears and washing are by no means the only OCD symptoms (see the page, "Common obsessions and compulsions and feared consequences"). Each OCD sufferer's own experience of the illness (the fears, beliefs and rituals) are different and are shaped uniquely by the sufferer's personal concerns. Sometimes obsessions and compulsions are difficult to separate as the compulsions themselves can have the form of purely mental (rather than physical) rituals. This is known as "Pure-O". A few other common obsessions and compulsions are given below.

To a non-sufferer of OCD such behaviour appears strange, unnecessary and excessive, and in most OCD cases a sufferer would agree with this assessment on a logical level. The problem is that OCD behaviour is driven largely on an emotional level, and these emotions are thought to originate from primitive parts of the brain which are difficult to control. In other words the obsessions and compulsions are forced by strong feelings rather than by evidence.

What is it like to have OCD?

To the outside world the sufferer in the above example is continually and unnecessarily washing their hands. To the sufferer the compulsion to wash is urgent and necessary to remove the uncomfortable feeling brought on by the contamination obsession. Some sufferers might describe having OCD with an analogy. Imagine that a stranger approaches you and places a gun to your head and tells you he might pull the trigger, but does not tell you when, or if the gun is loaded or not. You would experience anxiety and doubts akin to an OCD sufferer's daily battle with their illness.

If this were to happen literally in real life, doing the compulsions might be a useful survival instinct, but the OCD brain applies this instinct inappropriately to situations that are not harmful. Apart from this, the gun analogy can be a useful way of describing OCD to non-sufferers of the condition: OCD is like the constant presence of a metaphorical loaded gun to your head, while you remain powerless to escape the situation, despite trying very hard.

What OCD is not

OCD is not the transitory worry of everyday life even though the subjects of some 'normal' worries that people have can have things in common with those of OCD. If the anxiety is not chronic and extreme, or there is no associated ritualistic behaviour, then it may not necessarily be OCD (although many of the treatments used for OCD may well be effective at relieving these worries).

OCD is a label often mistakenly given to meticulous behaviour such as the act of arranging objects into a precise order. Being meticulous itself is not an illness, it may be instead a harmless part of an individual's personality, even though it may be referred to as a 'compulsive behaviour'. If such actions are not driven by the need to reduce anxiety then, again, it may not necessarily be OCD.

Why the specific worries with OCD?

The irony of OCD is that the form of the anxiety can mould itself to a sufferer's own values. For instance:

• • the person who cares passionately about being clean may feel dirty and is driven to perform cleaning rituals,

  • the person who is overly responsible may feel reckless and has to be sure that they will not be (or have been) responsible for a bad event,

  • the person who is overly concerned with safety and protection may feel dangerous and has to be sure everything is safe, and

  • the person who has strong religious or moral beliefs may feel that they have been unscrupulous.

Some specific examples of these points are given in the page, "Common obsessions and compulsions and feared consequences". The strong link between the specific form of OCD and the sufferer's personal values are thought to be an important reason why OCD can hold such strong power over an individual. The illness is 'conning' the sufferer into thinking that they have potentially violated their values and the OCD behaviour is a vain and desperate reaction to this. In short, OCD can make a sufferer think of themselves as an extremely bad person just by the way that they interpret intrusive thoughts and feelings that the vast majority of people have.

How can OCD affect a sufferer?

OCD is a significant, distressing, disabling and all-consuming illness which can seriously affect many aspects of a sufferer's life. Although its symptoms can sometimes outwardly appear quite strange, sufferers are not 'crazy'. It is a 'neurotic' rather than a 'psychotic' condition.

There is a misunderstanding amongst some people that OCD is a trivial condition to live with. OCD can genuinely devastate a person's life leaving them feel exhausted, lonely and helpless. It can lead to depression, unemployment, hospitalization, becoming house bound or even suicide. OCD can also significantly affect a sufferer's family, and their friends and colleagues.

Do you have OCD?

Only a doctor or clinical psychologist can diagnose OCD, but the process of diagnosis (and the onset of treatment) can be hastened if the sufferer is aware of the symptoms of OCD so that it can be suggested to the clinician. Here is an on-line test on the BBC web site, which may be helpful at suggesting a diagnosis.