Man flu is real. The idea that “man flu” is just an exaggeration has been circulating for years in memes and videos, poking fun at men for seemingly overreacting when they catch a cold or flu.
But let's set the record straight: men don't just appear to suffer more—they actually do experience viral infections more severely. Not only are men more prone to complications from these infections, but they are also more likely to die from them. This makes it particularly important for men to take better care of themselves when ill.
Research suggests that men have weaker defenses not only against viruses but also against parasites, bacteria, and fungal infections. They are more vulnerable to sepsis, a life-threatening immune response to infection. Testosterone, the primary male sex hormone, plays a role in this. While testosterone reduces inflammation, it also suppresses the thymus, where new immune cells are trained, leading to less robust immune cell production. The higher the testosterone level, the more severe the cold can be.
In contrast, estrogen, the dominant female sex hormone, enhances the activity of immune cells like T lymphocytes and macrophages, resulting in a more potent immune response in women. Moreover, women have greater numbers of certain immune cells, including plasma cells, regulatory T cells (Tregs), CD19+ B cells, mucosa-associated invariant T cells, and naïve CD8+ T cells, compared to men. Women also produce a higher surge of antibodies following vaccination and have longer-lasting immune memory than men.
However, this evolutionary advantage comes with a significant trade-off: women are far more prone to autoimmune disorders—making up 80% of all cases—due to their heightened immune activity.
From an evolutionary standpoint, these immune differences likely exist because women need stronger immune defenses through their reproductive role. A robust immune system helps protect the developing fetus by transferring antibodies. For men, it's less straightforward.
Some theories suggest that ancestral male behavior, such as increased risk-taking, exposed them to more infections, but paradoxically, this may have impaired their immunity. There's also the possibility of a trade-off between a strong immune system and reproductive fitness, with testosterone impeding the immune response and making men more susceptible to infections.
What does this mean for us today?
Men should take their infections more seriously and stand to benefit significantly from flu vaccinations. Women, on the other hand, should pay closer attention to measures that reduce the risk of allergies and autoimmune diseases.
Scientific basis for 'man flu' Nature Reviews Immunology volume 10, page 290 2010
The conneXion between sex and immune responses Nature Reviews Immunology volume 24, pages 487–502 (2024)
Gender-Specific Impact of Sex Hormones on the Immune SystemInt J Mol Sci. 2023 Apr; 24(7): 6302.