OCD is characterized by recurrent, unwanted and unpleasant thoughts (obsessions), and or repetitive, ritualistic behaviors, which the person feels driven to perform (compulsions). People with OCD know their obsessions and compulsions are irrational or excessive, yet find they have little or no control over them.
Typical obsessions include: dirt, germs and contaminations, fear of acting on violent or aggressive impulses, feeling overly responsible for the safety of others (for example, unreasonable fear of having run over someone with a car), abhorrent religious (blasphemous) and sexual thoughts, inordinate concern with order, arrangement or symmetry, inability to discard useless or worn out possessions, etc.
Typical compulsions include: excessive washing (particularly hand washing or bathing ), cleaning, checking and repetitive actions such as touching, counting, arranging in order, or hoarding. Ritualistic behaviors lessen the chances of distress from obsessions but only short term comfort at the long term cost of frequent ritual repetition.
(OCD description adapted with permission from OCA website).