
http://en.wikipedia.org/wiki/Obsessi...lsive_disorder
Obsessive–compulsive disorder
Obsessive–compulsive disorder (
OCD) is an 
anxiety disorder characterized by 
intrusive thoughts  that produce uneasiness, apprehension, fear or worry (obsessions),  repetitive behaviors aimed at reducing the associated anxiety  (compulsions), or a combination of such obsessions and 
compulsions. Symptoms of the disorder include excessive washing or cleaning, repeated checking, extreme 
hoarding, preoccupation with 
sexual, violent or religious thoughts, 
relationship-related obsessions, aversion to particular numbers and nervous 
rituals such as opening and closing a door a certain number of times before entering or leaving a room. These symptoms can be 
alienating and time-consuming, and often cause severe emotional and financial distress. The acts of those who have OCD may appear 
paranoid and potentially 
psychotic.  However, OCD sufferers generally recognize their obsessions and  compulsions as irrational and may become further distressed by this  realization.
The phrase obsessive–compulsive has become part of the English  lexicon, and is often used in an informal or caricatured manner to  describe someone who is excessively meticulous, perfectionistic, absorbed, or otherwise fixated.Although these signs are present in OCD, a person who exhibits them does not necessarily have OCD, but may instead have obsessive–compulsive personality disorder (OCPD), an autism spectrum disorder, or disorders where perseveration (hyperfocus) is a feature in ADHD, PTSD, bodily disorders, or just a habit problem.
Obsessions
Obsessions are thoughts that recur and persist despite efforts to ignore or confront them. People with OCD frequently perform tasks, or 
compulsions,  to seek relief from obsession-related anxiety. Within and among  individuals, the initial obsessions, or intrusive thoughts, vary in  their clarity and vividness. A relatively vague obsession could involve a  general sense of disarray or tension accompanied by a belief that life  cannot proceed as normal while the imbalance remains. A more intense  obsession could be a preoccupation with the thought or image of someone  close to them dying or intrusions related to "
relationship rightness." Other obsessions concern the possibility that someone or something  other than oneself—such as God, the Devil, or disease—will harm either  the person with OCD or the people or things that the person cares about.  Other individuals with OCD may experience the sensation of invisible  protrusions emanating from their bodies, or have the feeling that  inanimate objects are ensouled.
People with OCD understand that their notions do not correspond with  reality; however, they feel that they must act as though their notions  are correct. For example, an individual who engages in 
compulsive hoarding  might be inclined to treat inorganic matter as if it had the sentience  or rights of living organisms, while accepting that such behavior is  irrational on a more intellectual level.
Primarily obsessional
OCD sometimes manifests without overt compulsions. Nicknamed "Pure-O",  or referred to as Primarily Obsessional OCD, OCD without overt  compulsions could, by one estimate, characterize as many as 50 percent  to 60 percent of OCD cases. Primarily obsessional OCD has been called "one of the most distressing and challenging forms of OCD."  People with this form of OCD have "distressing and unwanted thoughts  pop into [their] head frequently", and the thoughts "typically center on  a fear that you may do something totally uncharacteristic of yourself,  something ...potentially fatal...to yourself or others." The thoughts "quite likely, are of an aggressive or sexual nature."
Rather than engaging in observable compulsions, the person with this  subtype might perform more covert, mental rituals, or might feel driven  to avoid the situations in which particular thoughts seem likely to  intrude.  As a result of this avoidance, people can struggle to fulfill both  public and private roles, even if they place great value on these roles  and even if they had fulfilled the roles successfully in the past. Moreover, the individual's avoidance can confuse others who do not know its origin or intended purpose, as it did in the 
case of a man whose wife began to wonder why he would not hold their infant child. The covert mental rituals can take up a great deal of a person's time during the day.
Some people with OCD perform compulsive rituals because they  inexplicably feel they have to, others act compulsively so as to  mitigate the anxiety that stems from particular obsessive thoughts. The  person might feel that these actions somehow either will prevent a  dreaded event from occurring, or will push the event from their  thoughts. In any case, the individual's reasoning is so idiosyncratic or  distorted that it results in significant distress for the individual  with OCD or for those around them. Excessive skin picking (i.e., 
dermatillomania) or hair plucking (i.e., 
trichotillomania) and nail biting (i.e., 
onychophagia)  are all on the Obsessive-Compulsive Spectrum. Individuals with OCD are  aware that their thoughts and behavior are not rational, but they feel bound to comply with them to fend off feelings of panic or dread.
 Some common compulsions include counting specific things (such as  footsteps) or in specific ways (for instance, by intervals of two), and  doing other repetitive actions, often with atypical sensitivity to  numbers or patterns. People might repeatedly wash their hands  or clear their throats, make sure certain items are in a straight line,  repeatedly check that their parked cars have been locked before leaving  them, constantly organize in a certain way, turn lights on and off,  keep doors closed at all times, touch objects a certain number of times  before exiting a room, walk in a certain routine way like only stepping  on a certain color of tile, or have a routine for using stairs, such as  always finishing a flight on the same foot.
 The compulsions of OCD must be distinguished from 
tics; movements of other 
movement disorders such as 
chorea, 
dystonia, 
myoclonus; movements exhibited in 
stereotypic movement disorder or some people with 
autism; and the movements of 
seizure activity. There may exist a notable rate of comorbidity between OCD and tic-related disorders.
 People rely on compulsions as an escape from their obsessive  thoughts; however, they are aware that the relief is only temporary,  that the intrusive thoughts will soon return. Some people use  compulsions to avoid situations that may trigger their obsessions.  Although some people do certain things over and over again, they do not  necessarily perform these actions compulsively. For example, bedtime  routines, learning a new skill, and religious practices are not  compulsions. Whether or not behaviors are compulsions or mere habit  depends on the context in which the behaviors are performed. For  example, arranging and ordering DVDs for eight hours a day would be  expected of one who works in a video store, but would seem abnormal in  other situations. In other words, habits tend to bring efficiency to  one's life, while compulsions tend to disrupt it.....