"They know they're not attracted to the same sex... but are consumed all day long with this battle."

Obsessive-compulsive disorder affects 2.2 million people in the United States alone, saddling them with compulsive behaviors, intrusive thoughts and unrelenting doubts.

People with OCD often worry about their safety, or that of loved ones, but for a certain subset of patients the obsession is with their sexual orientation.

Those with “homosexual OCD” (HOCD) are heterosexuals with a clear attraction to the opposite sex, but are consumed with worried they may be gay. The obsession makes daily life difficult and can prevent sufferers from having normal relationships.

In a sense, it’s similar to anorexia: A person can worry they are or will become overweight, even if they are dangerously then. The fear is not connected to the reality.

“These individuals suffer from pathological doubt. Even though they know that they are 100% straight, they second-guess it,” Dr. Jeff Szymanski of the International OCD Foundation told ABC News. “They might think, ’Wait a minute I spent too much time looking at that guy in the locker room. What does that mean?’ They get lost in the need to know, the need to be sure.”

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Szymanski says some sufferers seek out same-sex encounters as a “test” but are unenthusiastic or even traumatized by them. While Szymanski says a few of his patients come to realize they are indeed gay, true HOCD sufferers are aware, on a rational level, that they’re straight.

“They are consumed all day long with this battle. They can think of nothing else,” says psychologist Steven Brodsky. “A gay person doesn’t go through this battle.”

He lists examples of behaviors by people with HOCD:

* Imagining themselves in sexual situations and then observing their own reaction.

* Masturbating or having sex repeatedly just for the purpose of checking their own reaction.

* Checking the reactions or conversations of others to determine whether or not they’ve noticed them acting inappropriately.

* Reading stories by people who “came out” to see if they can relate.

* Repeatedly questioning others, or seeking reassurance, about their sexuality.

Fortunately, HOCD can be treated with medication and behavioral therapy.