In popular culture, "OCD" is loosely used to label a person who is quite particular about how neat or clean something should be. But such use is far from the clinical diagnosis of OCD or obsessive-compulsive disorder. Clinically, the disorder is defined by patterns of unreasonable thoughts and obsessions that lead to compulsions, or repetitive behaviors. Furthermore, a person is only diagnosed as having OCD if the obsessions and compulsions are so severe they interfere with every life.
The disorder is quite common, affecting about 1-3 percent of the population. And typically, sufferers develop OCD around a certain theme, such as being afraid of germ contamination.
Scientists don't know exactly what causes or triggers OCD, but we know that patients respond well to medications that target the neurotransmitter serotonin. The intersection of genetics and environment may also have an important role, as OCD is more prevalent among people with an affected first-degree relative.