People who are addicted to sex are drive to search more for new sexual images than their peers, according to a recent study.

An individual is a sex addict if they have difficulty controlling their sexual thoughts, feelings or behavior. It's a relatively common condition, affecting as many as one in 25 young adults.

"We can all relate in some way to searching for novel stimuli online - it could be flitting from one news website to another, or jumping from Facebook to Amazon to YouTube and on," researcher Dr. Valerie Voon said in a statement. "For people who show compulsive sexual behavior, though, this becomes a pattern of behavior beyond their control, focused on pornographic images."

For the study, researchers collected and analyzed data from 22 sex addicts and 40 "healthy" male volunteers. They were asked to complete a series of tasks.

In the first task, individuals were shown a series of images in pairs, including naked women, clothed women and furniture. They were then shown further image pairs, including familiar and new images, and asked to choose an image to "win £1" - although the participants were unaware of the odds, the probability of winning for either images was 50 percent.

The researchers found that sex addicts were more likely to choose the novel over the familiar choice for sexual images relative to neutral object images, whereas healthy volunteers were more likely to choose the novel choice for neutral human female images relative to neutral object images.

In a second task, volunteers were shown pairs of images -- an undressed woman and a neutral grey box -- both of which were overlaid on different abstract patterns. They learned to associate these abstract images with the images, similar to how the dogs in Pavlov's famous experiment learnt to associate a ringing bell with food. They were then asked to select between these abstract images and a new abstract image.

This time, the researchers showed that sex addicts where more likely to choose cues (in this case the abstract patterns) associated with sexual and monetary rewards. This supports the notion that apparently innocuous cues in an addict's environment can 'trigger' them to seek out sexual images.

"Cues can be as simple as just opening up their internet browser," Voon said. "They can trigger a chain of actions and before they know it, the addict is browsing through pornographic images. Breaking the link between these cues and the behavior can be extremely challenging."

The study is relevant to the context of online pornography.

"It's not clear what triggers sex addiction in the first place and it is likely that some people are more predisposed to the addiction than others, but the seemingly endless supply of novel sexual images available online helps feed their addiction, making it more and more difficult to escape," Voon said.

The findings are detailed in the Journal of Psychiatric Research.