Like ice cream, OCD comes in different flavors. This expressoin is a good metaphor for the idea that OCD can present as different symptom subsets. Some of these subsets are familiar to most people, but others are less common, and sometimes less recongizeable as OCD. Let's examine a few of these OCD flavors:
Washing, perhaps the most commonly known, is the vanilla of OCD. Obsessions have to do with becoming contaminated or in some way dirty from sources such as bodily fluids or chemicals, but even this most common of OCD flavors can have an unusual twist. So, for instance another person may be percieved as contaminated, not because of the sweat, urine, or microbes that might be on that person, but because that person is just who they are. The person with OCD might say: "If I come into contact with that person, something bad will happen," or "I will become that person," or "I will take on characteristics of that person." These obsessions result in the same kinds of avoidance and/or compulsive washing rituals as with the standard contamination fears.
Cleaning is related to washing, but the focus for the person with OCD is not so much one's body as a thing or a place (like a bedroom). The place or thing needs to be avoided or thoroughly washed, often in a ritualistic way, before the person with OCD will willingly come in contact with it.
Checking is another one of the well-known OCD presentations, but in addition to making sure that the locks are locked, the gas range is off, and the water faucet is not dripping, other, more subtle forms of checking exist. This is often in the form of repeated questions, and can be anything from, "Mommy, do you love me?" to "Are you sure it is safe?" Any repeated attempt to seek reassurance from another person is in fact a form of checking.
Repeating. If we continue with our ice cream metaphor, repeating might be a lemon or cherry flavor. While not one of the major standards, is clearly a common alternative, repeating can be a result of a specific obsession: "I thought the word 'death' to myself while I walked through the doorway, and so now I have to go back through it and repeat the behavior while thinking the word 'life' in order to 'erase' or 'undo' the previous activity." It can also be an attempt to merely ward off a bad feeling: "I need to repeat standing up and sitting down again until it feels 'right' and then I can stay seated."
"Hit and Run OCD," also called "MVA OCD" for Motor Vehicle Accident, is a specific instance of a checking behavior, which is so common that it should be mentioned separately. Drivers obsess that maybe they hit someone without realizing it when driving, and then drive back repeatedly to check the area for bodies and/or police or ambulance activity. They will then go home and check the papers and local TV reports for stories about hit-and-run accidents. An interesting twist about this particular OCD flavor is that people with it tend not to focus so much on whether they actually killed somebody, but more on whether or not they will be caught, punished, and publicly humiliated.
Orderliness involves things having to be exactly in their place, sometimes facing in a particular direction, or a specific distance from another object.
Need for Symmetry is the need for things to be equal, or equally weighted. The classic comic gag of the barber trimming a customer's mustache, and repeatedly finding that one side is longer than the other requring further trimming to "even it out" until there is no mustache left is a good example of this flavor.
Sexual obsessions, most commonly a fear that one is really gay or a pedophile when in fact there has been no sexual arousal, sexual fantasies, or sexual behaviors that would support this is yet another OCD twist. This flavor is more common than you might imagine, but sometimes will take a while for persons with OCD or family members to recognize that this problem is in fact an OCD flavor and not a struggle with sexual identity or sexual perversion.
Fear of loss of impulse control is yet another lesser known flavor. This behavior is more along the lines of a chocolate chip mint or cheesecake ice cream, the behavior is not always available but still out there. This involves the obsession that one will act out in some way, temporarily "go insane" and then just as quickly "snap out of it" and then be stuck with the consequences of their actions. Common presentations of this flavor include fear of stabbing one's family members, fear of blurting out inapporpriate statements or curse words in public, fear of jumping out of a moving car, or fear of stealing something from a store. Avoidance of potentially dangerous or embarrassing situations is usually the response, or else engaging in some kind of safety behavior, such as hiding the knives and locking them away or going places with a certain person who will "keep an eye" on the person.
Other flavors exist as well, or flavor twists where one or more flavors co-exist or intermingle. Hypochondriasis or health anxiety, Hoarding, Scrupulosity—the list goes on and on. The themes are always the same, however: A sense of uncertainty or incompleteness that needs to be righted in some way is the obsessive experience. This results in a compulisve or avoidant behavior designed to avert a danger or allow for normal functioning to return.