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Women's tears can have a negative effect on men's sexual desire, a new study suggests.

Scientists at the Weizmann Institute in Israel found that women's tears contain a "chemical signal", which reduces arousal in men.

Prof Noam Sobel told ����ý World Service radio that the signal reduced levels of testosterone and brain activity associated with sexual arousal.

His team now plan to study the effects of men's tears on women and men.

Testosterone

The researchers collected tears from female volunteers who cried while watching sad films.

Male volunteers then had the tears or a salt solution, without knowing which, placed under their noses on a pad, while they made judgements about images of women's faces. The experiment was then repeated, with those that had first been given the tears given the salt solution and vice versa.

The researchers found that the men who sniffed the tears judged the women's faces less sexually appealing than they did when they sniffed the salt solution.

The levels of testosterone - a hormone related to sexual arousal - in the men's saliva fell by 13% on average after they sniffed the tears, but stayed the same after sniffing the salt solution.

Their physiological state, as measured by skin temperature, heart rate and respiration, also fell after exposure to the tears.

MRI brain scans showed less activity in areas associated with sexual arousal after smelling the tears.

The researchers said the male volunteers could not distinguish the smell of the tears from that of the salt solution and that tears were odourless anyway.

"This study reinforces the idea that human chemical signals - even ones we're not conscious of - affect the behaviour of others," Prof Sobel said in comments published in the Science Express online journal.

He added that the results raised many questions, such as what the chemical giving out the signal was.