Being disgusted is a bigger passion killer for women than fear, according to new research.

The University of Portsmouth study is the first to compare how sexually aroused women are after being exposed to disgust and other kinds of negative stimuli. It is also the first to use medical equipment, in addition to self-reporting, to gauge sexual arousal after exposure to disgust.

Dr Diana Fleischman, of the University of Portsmouth's Department of Psychology, carried out the research when she was working at a North American university. She found that the more disgusted a woman was, the less sexually aroused she was likely to be.

Disgust is thought to be a protective emotion because it encourages humans to shun anything which could transmit disease, such as another person's blood or body fluids.

Dr Fleischman, an evolutionary psychologist, said: "Sex includes increased contact with body odours and fluids which, in other contexts, strongly suggest disease and would elicit disgust. Women are more vulnerable to contracting diseases through sex than men and show worse outcomes once infected so we should expect that women will be especially turned off when they are disgusted.

"It makes sense that sexual arousal and disgust would affect one another. Sexual arousal motivates us toward closeness with others and their bodies while disgust motivates us away. Given these competing motivations, every one of our ancestors had to overcome disgust in order to have sexual contact and reproduce.

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"Another prediction we made was that arousal would reduce disgust sensitivity. Previous studies have found that men and women who are exposed to sexually explicit images report less disgust. However our study is the first to measure blood flow to the genitals, which is necessary for sexual arousal, and how it interacts with disgust."

One of the most consistent differences science has found between men and women is that men are less sensitive to disgust than women, especially when it comes to sex. The researchers wanted to find out if women who are less likely to be disgusted would respond like men when sexually aroused.

The research found that women who are not very disgust-sensitive turn down their disgust sensitivity even further when they're sexually aroused whereas women who are highly disgust-sensitive show greater disgust when sexually aroused.

Dr Fleischman said: "When we are deciding whether to have sex there are trade-offs to consider. On the one hand you must have sex to reproduce, and on the other hand sexual encounters are risky for disease transmission. What our results suggest is that the story is more complicated for women and that women differ in how sexual arousal changes their disgust response."

The study included 76 heterosexual women aged 18-42.

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One group was shown disgusting images then asked to watch an erotic film. The second group watched an erotic film and were then were shown disgusting images. The third group were shown frightening images then shown an erotic film. The fourth group watched an erotic film and were then shown frightening images.

Images used to elicit disgust in the women taking part included diseased or injured humans and human corpses, faeces and people vomiting.

The erotic films watched were produced and directed by women and intended to be sexually appealing specifically to women.

The images designed to elicit fear included violent people, dangerous animals, weapons, heights, tornados and fire.

Before the experiments, all the women were asked to insert a vaginal photoplethysmograph -- a clear acrylic tampon-shaped device that measures blood flow to the vagina which indicates sexual arousal. They were also asked to report their own degree of arousal, disgust and fear after their tests.

Women who were exposed to disgusting images before watching an erotic film were three times less sexually aroused than those who had seen frightening images or those in the control group. There was no significant difference in the degrees of sexual arousal in the other groups.

Earlier studies have shown sexually aroused men are much less likely to find things disgusting. The latest study does not find the same straightforward story for women, but that was predictable, Dr Fleischman says, because of women's greater vulnerability to contracting disease through sexual activity.

The research is published in the journal PLOS One.