Men really do have an excuse for supposedly being wimpy about coughs and colds - their immune systems are not as strong as women's, research suggests.
A Canadian study indicates that the female sex hormone oestrogen gives women's immune systems added bite at fighting off infection.
Oestrogen seems to counter an enzyme which blocks the inflammatory process.
The McGill University study appears in Proceedings of the National Academy of Sciences.
These results demonstrate that women have a more powerful inflammatory response than men
Dr Maya Saleh McGill University
The researchers focused on an enzyme called Caspase-12, which is known to put a brake on the inflammatory process, the body's first line of defence against harmful invaders such as bacteria and viruses.
They worked on mice that lacked the Caspase-12 gene, and were thus extremely resistant to infection.
The human Caspase-12 gene was implanted into a group of male and female mice, but only the males became more prone to infection.
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The researchers concluded that oestrogen produced by the female mice blocked the expression of the human Caspase-12 gene.
They were also able to locate the precise place where oestrogen binds to the gene in order to block its activity.
Since the experiments were conducted using a human gene, the researchers are confident their work is applicable to humans.
Lead researcher Dr Maya Saleh said: "These results demonstrate that women have a more powerful inflammatory response than men."
The researchers believe women may have evolved a more robust immune system because of their key role in producing and nurturing young.
Their work raises the possibility of new ways to reinforce the immune system using genetic manipulation.
But writing in the journal, the researchers said: "A question remains: will men be amenable to the idea of being treated with an exclusively female hormone?"
Dr Leslie Knapp, of the University of Cambridge, said there was a substantial body of evidence to show that women were better at fighting infections than men.
She said: "Women are well known to be able to respond more robustly to infections, and to recover more quickly than men.
"In evolutionary terms it only takes one male to reproduce with lots of females, but females are much more important in terms of producing offspring."
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