The science behind "man flu"

"Man flu" is a term so ubiquitous that it has been included in the Oxford and Cambridge dictionaries. Oxford defines it as "a cold or similar minor ailment as experienced by a man who is regarded as exaggerating the severity of the symptoms." 1 Since about half of the world's population is male, deeming male viral respiratory symptoms as "exaggerated" without rigorous scientific evidence, could have important implications for men, including insufficient provision of care.

Despite the universally high incidence and prevalence of viral respiratory illnesses, 2 no scientific review has examined whether the term "man flu" is appropriately defined or just an ingrained pejorative term with no scientific basis. Tired of being accused of over-reacting, I searched the available evidence (box) to determine whether men really experience worse symptoms and whether this could have any evolutionary basis.

Methods I searched PubMed/MedLine, EMBASE, Cochrane, CINAHL, Web of Science, Scopus, and Google Scholar using combinations and variants of terms "man"/"male", "woman"/"female", "gender"/"sex", "influenza"/"flu", "viral", "respiratory", "common cold", "difference", "comparison", "intensive care." I read the abstracts of all articles found and narrowed articles down by relevance. References in each article were then hand searched to ensure comprehensiveness.

Of mice and men

Mice have long been accepted as good models of human physiology for medical research, 3 with records dating back to William Harvey in 17th century England. 4 Several studies show that female mice have higher immune responses than males. 5 6 This led to the hypothesis that sex dependent hormones have an important role in outcomes of influenza. Further studies suggest that oestradiol is implicated in this response in mice, 7 with one study concluding that the hormone reduces "responses associated with immunopathology" and enhances "responses associated with recruitment of innate immune cells…into the lungs." 8

However, another mouse study suggests that stress and corticosterone levels have a role, concluding that "the increase in infection-induced corticosterone levels demonstrated in females may have suppressed the behavioural symptoms of infection." 9

Lending further weight to the oestradiol theory, an in-vitro study sniffs at an underlying reason for man flu. Using human nasal epithelial cell cultures infected with seasonal influenza A, researchers showed that exposure to oestradiol or select oestrogen receptor modulators (SERMs) decreased influenza A titres in tissue...