© Magnific
October 23, 2026
Marianne Waldenfels
Man flu has been a running joke for years. But immunology research suggests there may be more to the cliché than male self-pity. What roles do testosterone, estrogen, and the X chromosome play?
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He is lying on the sofa with a temperature of 38 degrees, asking for tea and sympathy, convinced that this time it is serious. She had the same infection last week and went to work anyway. "Man flu" is one of the most popular clichés of the cold season — shorthand for a harmless cold that men supposedly blow out of all proportion.
For some years now, headlines have been circulating claiming that science has proven man flu exists. That is not entirely wrong. But the story behind it is more complicated — and the most revealing findings come not from the famous study, but from immunology research conducted in recent years.
In December 2017, Canadian general practitioner Dr. Kyle Sue of Memorial University of Newfoundland published an article in the British Medical Journal titled "The science behind 'man flu'." By his own account, the impetus was his own bout of flu and the accusation that he was exaggerating.
Sue compiled existing studies and concluded that men may not be exaggerating their symptoms at all, but rather have a weaker immune response to respiratory viruses. Among the evidence he cited:
His conclusion: the term man flu, used as an accusation of exaggeration, may simply be unfair.
At the time, the headlines made it sound as though researchers had produced new lab evidence. In fact, the piece appeared in the BMJ's traditional Christmas issue, in which the journal each year publishes scientifically grounded but tongue-in-cheek articles.
Sue did not conduct his own experiment; instead, he reviewed already published work. Some passages were clearly meant to be ironic: he suggested, for instance, that special recovery rooms equipped with large televisions and reclining chairs should be set up for sick men. His idea that a sick man's tendency to retreat would have protected him from predators in the Stone Age is also more of a thought experiment than an established finding.
US immunologist Prof. Sabra Klein of the Johns Hopkins Bloomberg School of Public Health, one of the leading researchers on sex differences in the immune system, commented at the time that the evidence was insufficient to declare man flu real. She also noted that lumping all men of all ages together was misleading. Sue himself acknowledged that rigorous studies on this question are lacking.
There is now considerably more evidence about why men and women respond differently to viral infections. A review article published in April 2026 in the journal Exploration of Immunology summarizes the state of research: on average, men face a higher risk of severe flu, while women tend to mount a stronger immune response.
It is worth noting that this primarily concerns genuine flu — that is, influenza. Whether men also suffer more from ordinary colds cannot be inferred from these findings.
A key factor lies in sex hormones. A team at Stanford University led by Dr. David Furman showed as early as 2014, in the Proceedings of the National Academy of Sciences (PNAS), that men with high testosterone levels produced fewer antibodies after the flu vaccine than men with lower levels. Estrogen, by contrast, tends to have an activating effect on many immune cells.
Just how strongly estrogen can influence the immune response is illustrated by a study from Johns Hopkins University published in September 2026 in the journal mBio. In younger women, the antibody response to the influenza virus H3N2 following vaccination was stronger than in men of the same age.
In people aged 75 and older, this difference was not observed. In supplementary laboratory experiments, the researchers found evidence that estrogen promotes antibody production in certain immune cells. The study was small, however, with 166 participants, and the older group received a high-dose vaccine.
Many genes that regulate the immune system are located on the X chromosome — and women typically have two copies of it, while men have one.
A review article published in March 2026 in the journal Nature Immunology from Sabra Klein's research group describes two key mechanisms: the differential activity of X-linked genes in immune cells, and the influence of sex hormones on innate and adaptive immunity.
Both contribute to men and women processing viral infections and vaccinations differently. These differences do, however, shift over the course of a lifetime.
A more reactive immune system is not always an advantage. Women more frequently report reactions after flu vaccinations — such as pain at the injection site, fatigue, or fever — as the review in Exploration of Immunology describes.
Autoimmune diseases, in which the immune system turns against the body itself, also occur significantly more often in women.
For public health purposes, another finding may matter more than the question of who complains more. A US study by the IVY Network involving more than 17,000 hospital patients, published in the journal Vaccine, found significant differences in flu vaccine effectiveness.
In people aged 50 and over, the estimated vaccine effectiveness against flu-related hospitalization was 48.5 percent in women, compared to 26.2 percent in men. Whether this gap is similarly large in other flu seasons remains to be seen.
This by no means suggests that the vaccine offers little benefit for older men. On the contrary: vaccination remains especially important precisely when the risk of severe illness is elevated.
The Standing Committee on Vaccination recommends annual flu vaccination for all people aged 60 and over, as well as certain at-risk groups, including those with chronic illnesses. Vaccines specifically tailored to older adults are also available for people aged 60 and over.
How much higher vaccination rates could matter is illustrated by figures from the Robert Koch Institute: in the 2024/25 season, only just over a third of people aged 60 and over in Germany were vaccinated against flu.
The suffering man on the sofa is not necessarily exaggerating. With genuine flu, men face on average a higher risk of a severe course than women. Whether they also feel worse with an ordinary cold is something science cannot yet answer definitively.
There is no evidence that men complain more than women with the same infection, but there is no clear evidence to the contrary either. How symptoms are experienced and described depends not only on biology, but also on habits and gender roles.
Man flu can no longer be dismissed as a mere joke, however. A little sympathy is entirely justified.
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