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There’s swine flu and bird flu, but _man flu_? Don’t worry, it’s (probably) not contagious. It’s more a humorous label for the tendency of many men to act like big babies, claiming they

suffer much more than women when they have the flu. There’s even a tongue-in-cheek website about the condition. But men may have the last laugh. Previous animal studies have found that male

and female immune systems react differently to attacks by viruses, and now, recent studies add fuel to the fire. An analysis published this month in _The BMJ_ (formerly the _British Medical

Journal) _looked at studies of various viruses and respiratory illnesses in men and women, and concluded that "men may not be exaggerating symptoms but have weaker immune responses to

viral respiratory viruses, leading to greater morbidity and mortality than seen in women." Earlier this year, research conducted on lab mice at the University of Ottawa’s

NeuroImmunology, Stress and Endocrinology Lab suggested infections may indeed be more severe in men than in women. The study was published in the journal of _Brain, Behavior, and Immunity._

The scientists injected male and female mice with bacteria that triggered an immune response similar to what the body experiences with a flu infection, said coauthor Nafissa Ismail, the

lab’s director. “The symptoms were a lot more intense in adults males than they were in adult females,” Ismail wrote in an email. The men suffered greater drops in body temperatures (typical

of the feverish chills that accompany the flu) and had more signs of inflammation in their bloodstream. They even looked more miserable — droopy-eyed, shivering and huddled together,

researchers reported. The fact that the men had a more acute reaction than the women “lends support to the idea that man flu really exists,” Ismail said. So why do men’s symptoms seem to be

worse than women’s? Ismail and her colleagues suggest it’s because testosterone and estrogen affect the immune system differently. Estrogen revs up the immune system, so women typically feel

worse initially but recover faster. Testosterone, however, slightly suppresses the immune system, so men tend to stay sicker longer. (In the study the male mice took an average of 48 hours

to recover, whereas the female mice took 24 hours.) Obviously, a study on mice doesn’t prove that the same reactions occur in humans, but it does suggest that hormones and other factors may

cause gender differences in how the body responds to illness. The one thing the researchers couldn’t detect, though, was whether those male mice whined more about their symptoms.