Last year, Melbourne, Australia, experienced an unprecedented “thunderstorm asthma” event. Some 10,000 people were rushed to the hospital, struggling to breathe, with at least nine deaths. No breakdown has been published, but if this resembled most other such events, two-thirds of those affected were women. Adult women are roughly twice as likely to suffer asthma as men, even though boys get it more frequently than girls. Now, a research institution based in the heart of Melbourne has laid the blame for this difference with testosterone.

The hormone testosterone gets blamed, or credited, with all sorts of differences between men and women, often falsely. However, Dr Cyril Seillet and colleagues at the Walter and Eliza Hall Institute found it also plays an unexpected role in asthma.

In the Journal of Experimental Medicine, the researchers report that testosterone suppresses the production of innate lymphoid cells (ILC2s). Since ILC2s can react to pollen, dust mites, or cigarette smoke by producing inflammatory proteins that trigger asthma attacks, the reduction in these cells that men experience after puberty makes them less likely to suffer the attacks. “In males, you have less ILC2s in the lungs and this directly correlates with the reduced severity of asthma," Seillet said in a statement.

The discovery makes finding other ways to suppress ILC2s a natural line of research to tackle the rising rates of asthma. "Current treatments for severe asthma, such as steroids, are very broad based and can have significant side effects," said co-author Professor Gabrielle Belz. 

Seillet told IFLScience the researchers are looking for compounds that modulate ILC2s without the effects testosterone has on other tissues in the body. He said that a number of molecules already used for other purposes have potential, and testing is underway.

Naturally, ILC2s would not have survived in the body if their effects were entirely negative, and their reaction to dust mites gives a hint of their evolutionary function. Seillet told IFLScience they have an important role in protecting against parasite infections, as well as having an influence on obesity. Theoretically, it might be expected that men's lower ILC2 production would increase vulnerability to parasites, but Seillet said this has yet to be investigated.

Seillet added that ILC2s and testosterone are not the whole story when it comes to explaining asthma. “Asthma is multifactorial,” he told IFLScience. “It is triggered by environmental cues and influenced by genetic background.” However, Seillet and his colleagues investigated the difference observed between rates in men and women, for which testosterone's influence on ILC2s proved explanatory.