Obsessive Compulsive Disorder (OCD) is an anxiety spectrum disorder which is chiefly characterised by the occurrence of unwanted and intrusive (interfering) obsessive thoughts or distressing images usually accompanied by compulsive behaviours performed to neutralize the obsessive thoughts or images or to prevent some dreaded event or situation. 
Obsessions involve persistent and recurrent intrusive thoughts, images or impulses that are experienced as disturbing and inappropriate. People with such obsessions try to resist, suppress or neutralize them with some other thought or action. Obsessive thoughts consist most often of contamination fears, fears of harming oneself or others, need for symmetry, sexual obsessions and obsessions concerning religion or aggression. Compulsions can involve either overt repetitive behaviours like hand washing, checking or arranging things in an order or more covert mental acts like counting, praying or saying certain words silently. A person having OCD would realise that the obsessions are a product of his own mind but still feels compelled or driven to perform the compulsive act to “prevent something bad from happening”.
Prevalence of OCD
OCD is a fairly common psychological problem with a lifetime prevalence rate of 1-2% globally, i.e. 1 in every 100 persons could experience an episode of OCD at least once in their entire lifetime. Although the characteristics of OCD are very common and experienced by all of us during our daily lives, what makes it a disorder is the severity and the persistence of disturbing thoughts and actions over a period of time.
Like any other psychological illness, there could be various factors causing OCD. The biological factors could be genetic vulnerabilities, heritability, or brain and neurotransmitter abnormalities. Studies suggest that the dysfunction of certain brain areas like orbital frontal cortex, cortico-basal-ganglionic-thalamic circuit could be responsible for the illness. Serotonin, an important neurotransmitter in the brain, has also been shown to be significantly involved in the development of OCD. 
There are many psychological theories explaining the aetiology of OCD. According to them, some of the most significant psychological factors responsible for causing and maintaining the illness are - faulty thinking process, irrational beliefs, faulty learning and misinterpretation of intrusive thoughts. Obsessive thoughts lead to significant anxiety which the person finds extremely distressing. In order to get rid of this unpleasant feeling, the person performs the action which reduces the anxiety. This acts like a positive reinforcement and hence an unending, vivious cycle is formed.
As mentioned above, we all experience intrusive thoughts in our day-to-day lives but people with OCD seem to have an inflated sense of responsibility and so misinterpret these thoughts as being very important and significant which could lead to catastrophic consequences. In addition to this, stress is another important aspect that needs to be considered while talking about any psychological problem. Although stress does not seemingly cause OCD, it can trigger the onset of the illness in a person who is biologically or psychologically predisposed to it and can worsen the symptoms in a person having the disorder.
Before we initiate the therapy process, it is imperative that we make a complete assessment of the nature, intensity and frequency of all the obsessions and compulsions present in the individual. Assessment consists of detailed clinical interview, self-monitoring, homework assignments and direct observation by the therapist. Cognitive Behaviour Therapy (CBT), wherein the focus is on replacing the faulty thought processes with the more appropriate, logical and adaptive thinking patterns, is the most widely employed and accepted form of therapy for treating OCD. Some of the techniques frequently employed in the treatment of OCD are-
Exposure-Response Prevention (ERP) – Avoidance is often the most common response to anxiety provoking stimuli or situations. The more we try to deal with the problem by avoiding, the more real it seems and the more the thoughts get stuck in our mind. This is exactly what happens in OCD also as the person tries to avoid the obsessive thoughts by neutralising them either through an outward compulsive action or some covert ways. This technique works on the principle that the best way to deal with such thoughts is to get used to them without doing the compulsive actions and avoidance. It requires the person to get more in contact with the things he /she dreads, get used to them and eventually realise that the things that worried him/her actually never happen. The person is “exposed” to the anxiety provoking stimuli without being allowed to perform any activity to neutralise it (“response prevention”). The anxiety might increase initially but will gradually reduce on its own without performing the compulsive or neutralising action. This in turn would break the faulty association that was formed between the obsession and compulsions. 
Some Dos and Don'ts as part of the therapuetic process which are very effective in treating the problem of OCD:
DOs                    DON'Ts
  • Let the thought/image/impluse come and let them go.
  • Do not try to stop the thought/image/impulse as it has a paradoxical effect. 
  • Be with the anxiety
  • Do not avoid the thought/image/impulse
  • Accept that these thoughts/images/impulses are not from your own mind, but because of OCD
  • Do not try to control the thought/image/impulse
  • A thought is just a thought, and not reality. Just observe it as an audience without engaging with them.
  • Do not distract yourself as it will provide provide relief but only temporarily.
Another important point worth noting is that guilt is the best friend of OCD; whenever there is guilt attached to obsessions, it will exacerbate the problem. Hence, it is important for the person to understand that simply having an obsessive thought (for instance – sexual images) is not equivalent to having actually done that in reality. We all experience such unpleasant or unwanted thoughts, impulses or images almost everyday and so there is nothing abnormal in it. It is just a thought and has no relevance till the time we attach some meaning to it or in case of OCD, there is anxiety due to the increased sense of responsibility. OCD can be an extremely debilitating and distressful illness for the person suffering from it as it hampers the functioning in various aspects. But there is hope as it is definitely a treatable illness with a combination of pharmacological and psychotherapeutic interventions. Homoepathic medicines are very efficient in treating OCD in combination with psychotherapy.