Obsessive-Compulsive Disorder, is a type of anxiety disorder. A person who has OCD has recurring or repeated obsessions and/or compulsions. Obsessions are thoughts, ideas, or images that persist in the mind. Compulsions are mental acts or behaviours that are carried out repeatedly. These obsessions and compulsions are severe enough to be time-consuming. They may also cause a fair amount of distress or impairment. The impairment can interfere with everyday activities.
Many people have a mild degree of obsessional behaviour. Frequent checking if the door is locked, where the keys are or that the gas is turned off. This level of problem is usually regarded as normal. However, when the issues become so severe, that they prevent them from living life to the full, then it would be defined as Obsessive-Compulsive Disorder (OCD). Where the issues are related to people's health or body, we would define it as Health Anxiety, or Body Dysmorphic Disorder (BDD).
Currently the cause of OCD AND BDD is unknown. Many theories exist but much more research is required before there will be an answer to this question, but the rituals or compulsive thoughts which are meant to prevent or reduce anxiety related to your obsessions or prevent something bad from happening bring no pleasure and may offer only a temporary relief from anxiety. The more you try to rid yourself of doubts, the more they tend to play on your mind.
The most effective therapy for OCD are Cognitive Behavior Therapy supported by Clinical Hypnotherapy . More specifically, the most effective treatments are Exposure and Response Prevention (ERP) therapy, a type of CBT and Clinical Hypnosis, which has the strongest evidence supporting its use in the treatment of OCD.
Persons with an obsession will have intrusive, unhelpful or even harmful worry and anxieties and develop behaviour which they perceive as reducing these anxious feelings. However, these thoughts can become so overpowering that it causes feelings and behaviour that creates even greater anxiety. This cycle of perpetual anxiety and behaviour impacts greatly on their lives, often preventing them from living their life to the full or in severe cases, even dictating everything they do.
Once a person develops such an obsession, it can be difficult to break the cycle. The more the intrusive thoughts take over, more anxiety is generated and the need to regain control increases. Subsequently leading the person to repeat the avoidance or repeat behaviour.