Sorry guys, but women are just better at fending off colds than you. wavebreakmedia/Shutterstock

To most, “man flu” is thought of as a pejorative, a way of teasing men who are complaining perhaps a little too much about the cold or influenza virus they’ve picked up. However, a new piece of research suggests that man flu may be an actual condition that men suffer from. As revealed in a study in the American Journal of Physiology – Lung Cellular and Molecular Physiology, it has everything to do with estrogen – specifically, men’s lack of it.

For this study, the influenza A virus was used. The amount of replication a virus undergoes in a host is roughly analogous to how severe the infection is. In order to see if influenza A infected men and women differently, the team of researchers from Johns Hopkins University intentionally infected nasal cells – those that are primarily targeted by the virus – from a range of male and female donors.

Man flu is real, then, but there’s nothing you can do about it. bikeriderlondon/Shutterstock

For this particular study, the researchers wished to know if estrogen had any effect on the replication of the virus. This sex hormone is mostly responsible for the development and regulation of the female reproductive system, although it also plays a role in the development of young male adults. Women do have more estrogen than men, however, and the researchers suspected this may have something to do with why “man flu” is a term without a female equivalent.

The researchers first exposed the uninfected nasal cells to estrogen and a class of drugs called selective estrogen receptor modulators, or SERMs. Cell receptors that are activated by estrogen can also be stimulated by SERMs, which produce estrogen-like effects. The treated nasal cells were then put into contact with the influenza virus.

They found that any female cells treated with estrogen or SERMs from 72 to 24 hours prior to infection showed a far greater resistance to infection, with viral loads within the nasal cell cultures far lower than male cells also treated with estrogen. This strongly suggests that estrogen has female-specific antiviral qualities, and that even after treatment, male nasal cells are no more resistant to infection.

The reasons behind this are not yet clear, but the researchers note that it may have something to do with estrogen’s ability to reduce the cell’s metabolic rate, which could slow down the ability of the virus to replicate itself.

Sabra Klein, lead author of the study, noted in a statement that “other studies have shown that estrogens have antiviral properties against HIV, Ebola and hepatitis viruses.” What makes her study unique is that they were able to directly identify the sex-specific effect of estrogen.

“We see clinical potential in the finding that therapeutic estrogens that are used for treating infertility and menopause may also protect against the flu,” she added. As for men suffering from “man flu,” however, it looks like estrogen won’t help them out in the slightest.