A new study says that it is the immune systems of macho men that attract women rather than their good-looking faces and chiseled abs.
Men with high levels of the sex hormone testosterone are considered as more hunky - and these same men have stronger immune responses.
The findings have suggested that women may be attracted to manly facial types because the macho look indicates good health.
Researchers led by Fhionna Moore of Abertay University in the United Kingdom recruited 74 Latvian men in their early 20s to give blood samples right before and one month after their first dose of the Hepatitis B vaccine, the Huffington Post reported.
The vaccine activates the immune system to create antibodies against the virus. The researchers measured these levels of antibodies as well as testosterone levels and levels of the stress hormone cortisol.
Next, 94 Latvian women, also in their early 20s, rated photographs of each man on a 10-point scale of attractiveness. The researchers then searched for links between the immune response as measured by Hepatitis B antibodies, hormone levels and attractiveness.
They discovered that high testosterone correlated with both sexy faces and a strong immune response.
Men with the strongest immune responses were rated as better looking than those with weak immune responses. The link between testosterone and hotness was strongest in men with low levels of the stress hormone cortisol, indicating that stress might take a toll on the immune system, and thus women's ratings of attractiveness.
While much research has hinted at a relationship between testosterone and the immune system, this study is the first to directly associate women's opinions of a man's looks with the strength of his immune system.
The study has been published in the journal Nature Communications.