Obsessions and compulsions present in an infinite number of ways focusing on a number of themes: contamination, aggression, harm avoidance, distasteful sexual thoughts, religious or moral issues, a need to know things, a need for symmetry, to name only a few. Contamination fears are the most common obsessive thought, and cleaning and checking are the most commonly reported compulsions. Multiple obsessions and compulsions are common. In addition, the theme of the obsessions and compulsions may change over the course of the illness.
The mean age at onset of OCD is 19.5 years, and 25% of cases start by age 14 years. Onset after age 35 years is unusual but does occur. Males have an earlier age at onset than females: nearly 25% of males have an OCD onset before age 10 years. The onset of symptoms is typically gradual, however, acute onset has also been reported.
How OCD Differs from Normal Behavior
Everyone obsesses about some event from time to time. The diagnosis of OCD, however, generally requires that obsessive thoughts occur for more than 1 hour each day. In addition, obsessions of OCD do not suddenly start and stop with a specific event. If you are worried about a loved one being treated for cancer you may think about the possible outcomes for more than 1 hour each day but after the cancer enters remission, you probably reduce your thinking or stop worrying about it. Someone with OCD may reduce their obsessions after an event but they will generally focus on some new topic at the same level of intensity.