Does it seem strange that we will enthusiastically kiss an attractive person’s mouth, with tongues intertwining and saliva going everywhere, but that we might wrinkle our nose up at the idea of using that same person’s toothbrush?

Our disgust response to other people’s bodily fluids (among other things) is thought to be an evolutionary adaptation for avoiding disease, but our most important evolutionary task – reproducing – involves exchanging bodily fluids in a pretty messy way.

This paradox is investigated in new research by Charmaine Borg and Peter de Jong at the University of Groningen, published yesterday in the open-access journal PLoS ONE.

Borg and de Jong wanted to know how we find sex so pleasurable despite it involving so much stuff that we tend to find disgusting in other contexts – stuff such as saliva, sweat, vaginal fluid, and semen.

One possibility is that being sexually aroused simply makes us less disgusted by the stuff that normally disgusts us. If this were true, a further question would be whether sexual arousal affects our disgust only for sex-related stuff or for all disgusting stuff.

To investigate these possibilities, Borg and de Jong randomly assigned 90 female volunteers into three separate groups. One group was shown a “female-friendly” erotic video, in order to sexually arouse the participants. As a control, another group watched an exciting video without sexual content (an extreme sports video), and a third group watched a video with no exciting or sexual content at all (a scenic train ride).

All participants were then asked to perform 16 tasks that would normally elicit a reaction of disgust. Some tasks were sex-related – such as lubricating a vibrator – and some were not – such as taking a sip of juice from a cup with an insect in it.

The researchers looked at how disgusted participants said they were by the idea of doing the task (self-report) and also at whether they ended up actually doing the task.

The first key result was that the sexually aroused group (i.e. those participants who had watched the porn) reported less disgust at the disgusting tasks, and more often actually completed them compared with the two control groups. This suggests that, indeed, being sexually aroused decreases our disgust sensitivity and allows us to do dirty things.

But does this lowering of our disgust sensitivity apply only to sex-related dirty things, or to dirty things in general?

Intriguingly, participants in the sexually aroused group were less disgusted by (and more willing to do) all sorts of disgust-eliciting tasks, not just sex-related ones. So sexually aroused participants were more likely to go through with lubricating a vibrator, but also drinking an insect-in-juice cocktail.

This study is fascinating and fun, and contributes to an explosion in interest and understanding regarding the mechanisms and functions of disgust. But the study might also have special relevance to the causes and consequences of sexual dysfunctions.

If sexual arousal decreases disgust and allows us to engage in the dirty business of sexual intimacy, what happens when sexual arousal decreases or disappears – due to anxiety or ageing, for instance?