A new study has revealed that "Man flu" is real and they have weaker immune systems, with less resistant to pneumonia and other respiratory illnesses.
Scientists from Harvard University have discovered that the female sex hormone oestrogen fortifies the immune system, and men are suffering for its absence, The Independent reported.
Professor Lester Kobzik at the Harvard University School of Public Health said female mice demonstrated increased resistance to infection, linked to the enzyme nitric oxide synthase 3 (NOS3) activated by the release of oestrogen.
The research showed that a simple dose of oestrogen was capable of curing both male and female mice of bacterial pneumonia.
The discovery could be used to improve resistance to common and serious lung infections and prevent flu from developing into pneumonia.
The study is published in Life Sciences medical journal.