OCD stands for obsessive compulsive disorder.
Obsessions are repetitive thoughts, ideas, images which the person knows are wrong but cannot stop them resulting in marked anxiety and unease.
Compulsions are repetitive acts either imaginary or physical done in response to an obsession eg repetitive hand washing, cleaning, detail to symmetry, hoarding etc.
Many factors might play a part:
Ocd is sometimes inherited, so it can run in the family. Stressful life events bring it on in about one in three cases. Life changes - when you have to take on more responsibility, such as puberty, the birth of a child, or a new job, if you have ocd for a long time, some experts think that an imbalance of a brain chemical called'serotonin' (also known as 5ht) may be involved. You are a neat, meticulous, methodical person – but go too far. If you have particularly high standards of morality and responsibility, you may feel bad when you have unpleasant thoughts. So, you watch out for them – which makes them more likely to happen.