Obsessive Complusive Disorder

OCD is short for Obsessive Compulsive Disorder. It is a type of chronic anxiety disorder, most often characterized by, Obsessing, Repetitive thoughts, and distressing.
The Compulsions are a kind of "ritual" the person feels compelled to do, to alleviate the obsessions. For example, if I have thoughts about hurting people, then I can void those thoughts by opening and shutting a door 13 times, a certain way.

It is important to know that people who suffer from OCD do not have control over their obsessions and the compulsions are therefore hard to stop. The best way to help someone with OCD is to support him or her, and not bring attention to the disorder.

OCD can manifest itself in numerous ways, but there are some symptoms that are more common than others.

Tasks
The compulsion to perform certain tasks can be an obsessive behavior, or a "remedy" to another obsession. Often these tasks must be completed before the person can move forward. For example, I need to count all the ceiling tiles 5 times, to void a previous thought about praying. If I am rushed to complete this task, it will not be done right, and thus will have to be repeated. Likewise if I am interrupted during the task.Another example is getting "stuck" in a doorway. I am entering or leaving a room, and I must go through the door a certain way. I can't explain it, it just has to feel right. If I don't go through right, I can not go into the room. There have been reports of people being "stuck" for hours.

Unwanted or intrusive Thoughts
Intrusive thoughts are unwelcome, involuntary thoughts, images or unpleasant ideas that may become obsessions, and are upsetting or distressing, and can be difficult to be free of and manage. Intrusive thoughts, urges, and images are of inappropriate things at inappropriate times, usually falling into three categories: inappropriate aggressive thoughts, inappropriate sexual thoughts, or blasphemous religious thoughts (thinking that God does not exist, etc.). Most people experience these thoughts; however, when they are associated with OCD or depression, they may become paralyzing, anxiety-provoking, and persistent. Many people experience the type of unpleasant or unwanted thoughts that people with more troubling intrusive thoughts have, but most people are able to dismiss these thoughts. When intrusive thoughts co-occur with OCD, patients are less able to ignore the unpleasant thoughts and may pay undue attention to them, causing the thoughts to become more frequent and distressing. People will often perform a Task or some sort of Compulsion to rid themselves of the thoughts.

Contamination
This is in my experience, one of the more common obsessions. Many OCD sufferers have a fear that certain substances, usually produced by the human body, are almost deadly to the touch, and they have an unreasonable fear of contamination other people or things with these germs. Likewise, they also have the fear of contaminating themselves, usually fearing some horrible illness resulting from it.
When I was a child, I would spend hours washing my hands, so much that they became chapped and bloody. Why did I do this? Because I was afraid of either becoming ill from touching something another person had touched, or that my own germs would infect others.

Not every person who has obsessive thoughts or behaviors has OCD; it is quite common for the average person to experience a few uncontrollable thoughts.
To be diagnosed with OCD, a person must have either obsessions or compulsions alone, or obsessions and compulsions
Here is a list of the recognized components one must have to be diagnosed as OCD:

Obsessions

• Recurrent and persistent thoughts, impulses, or images that are experienced as intrusive and that cause marked anxiety or distress.


• The thoughts, impulses, or images are not simply excessive worries about real-life problems.
  The person attempts to ignore or suppress such thoughts, impulses, or images, or to neutralize them with some other thought or action.


• The person recognizes that the obsessional thoughts, impulses, or images are a product of his or her own mind, and are not based in reality.

Compulsions

• Repetitive behaviors or mental acts that the person feels driven to perform in response to an obsession, or according to rules that must be applied rigidly.


• The behaviors or mental acts are aimed at preventing or reducing distress or preventing some dreaded event or situation; however, these behaviors or mental acts are not actually connected to the issue, or they are excessive.

As to how a person gets OCD, there are two major theories:
Psychological
Scientists suggest that the behaviour is carried out to remove anxiety-provoking intrusive thoughts. Unfortunately this only brings about temporary relief as the thought re-emerges. Each time the behaviour occurs it is negatively reinforced by the relief from anxiety, causing the sufferer to believe that the remedy worked. For example, after touching a door-knob a person might have the thought that they may develop a disease as a result of contamination. They then experience anxiety, which is relieved when they wash their hands. This might be followed by the thought "but did I wash them properly?" causing an increase in anxiety once more, the hand-washing once again rewarded by the removal of anxiety (albeit briefly) and the cycle being repeated when thoughts of contamination re-occur. The distressing thoughts might then spread to fear of contamination from a chair, for example, someone might have touched the chair after touching the door handle.
Biological
Another theory is that OCD is biological. Meaning that it can be a result of a persons genetics, or even passed down through a family. There is still a lot of research needed in this area, but the theory is proving true in at least some cases.

There are several different methods of treatment for OCD, each different in that every person reacts differently. Medication and Behavioral Therapy (Physiologists) are two commonly used treatments. Science is constantly coming up with new medications to treat various symptoms of OCD, and many patients have, with the help of their doctor, found a combination that works for them.
The downside to medication is the chance of side effects and the possibility of illness due to drug mixing, or patient intolerance. That said, most sufferers choose to take medication to help manage their OCD.
There are dozens of medications currently approved for treatment of OCD, and new ones are being developed.

Some places that helped me gather my infomation, and other very nice sites.

http://www.anxietypanic.com/ocdfacts.html
http://www.healthyplace.com/Communities/Ocd/sandra/facts.htm

and of course Wikipedia.
I also used several of my books to make this lens.