Intrusive thoughts, images or urges about hurting someone, such as a partner, a child or a stranger. The thoughts are unwanted and horrifying to the person having them, which is exactly why they cause so much distress. Having them does not mean you will act on them.

Common compulsions: hiding knives, avoiding loved ones, mentally reviewing, seeking reassurance. New parents are especially likely to be caught off guard by this theme.

A sudden fear that you struck someone while driving without noticing. The doubt can arrive at the wheel or hours later.

Common compulsions: retracing a route, checking the news for accidents, checking the car for damage, or avoiding driving.

Persistent fear of having sinned, offended God or broken a moral rule. It often attaches to whatever a person values most, so it affects deeply faithful and deeply ethical people alike.

Common compulsions: excessive praying, repeated apologies, seeking reassurance from clergy, avoiding anything that feels “impure.”

A strong need to admit minor or imagined wrongdoing to a partner, parent or friend. Confessing brings brief relief, then the urge returns. It often overlaps with scrupulosity and relationship OCD.

Unwanted, disturbing thoughts or images involving children, along with intense fear of being a dangerous person. Shame keeps many people from speaking up. These thoughts are the opposite of what the person wants, and a trained OCD therapist will not be alarmed by them.

Common compulsions: avoiding children, self-testing, checking for arousal, confessing.

Nagging uncertainty about whether your partner is “the one,” whether your love is real enough, or whether you are attracted enough. Ordinary doubts become an all-consuming search for certainty.

Common compulsions: comparing your relationship to others, testing your feelings, asking friends for verdicts, mentally listing pros and cons.

Intrusive doubts about your sexual orientation that feel urgent and unsettling. It can affect anyone, whatever their actual orientation. The distress comes from the doubt itself, not from being gay, straight or bisexual.

A nickname for OCD that seems to have obsessions but no compulsions. In nearly all cases there are compulsions, just hidden ones: mental review, silently repeating phrases, or reassuring yourself. Pure O is usually harm, relationship, sexual or religious OCD in disguise.

Overwhelming fear of germs, dirt, chemicals or illness, including sexually transmitted infections. Washing and avoidance can take up hours and shrink a person’s world.

Mental contamination is a variation: feeling dirty because of a thought, memory or interaction rather than actual contact. It can feel like it cannot be washed away.

Recurring fear that you have, or will get, a serious illness. Unlike ordinary worry, it drives repetitive body checking, late-night symptom searches and repeated medical visits, none of which bring lasting comfort.

Repeatedly confirming that stoves are off, doors are locked or appliances are unplugged, driven by fear that something terrible will happen if you are not careful. Checking often increases doubt rather than easing it.

A need for things to look, sound or feel exactly right. You may re-do an action, straighten an object or repeat a movement until an uncomfortable sensation lifts. It is often driven by a sense that something is “off,” rather than by a specific fear.

Compulsions that involve physical movements, like tapping or touching in a set pattern, and can look a lot like tics. It is more common in people who also have a history of tics.

Obsessive questioning about reality, consciousness, death or the meaning of life. Where most people shrug at these questions, someone with OCD feels they must solve them immediately. It is often mistaken for generalized anxiety or depression.

Endlessly replaying something that really happened, such as a conversation or an awkward moment, and fearing you did something wrong or harmful. Compulsions include mental review and asking others what they remember.

Recurrent pulling of hair from the scalp, brows, lashes or elsewhere, resulting in noticeable loss and distress. Habit reversal training is effective.

Picking at skin to the point of wounds, infection or scarring, despite wanting to stop. It responds well to behavioral therapy.

Body-focused repetitive behaviors that are harmless in small doses. If they cause bleeding, pain or embarrassment, treatment can help.