It might not be your good looks or masculine features that drive your woman wild. According to a new study from researchers at Abertay University in the Scotland, women are attracted to men with a strong immune system.

Fhionna Moore, a psychology professor and lead study author, and her team of researchers took blood samples from 74 Latvian men in their early 20s right before and one month after their first dose of the hepatitis B vaccine (which makes the immune system create antibodies against the virus). Scientists then measured the antibody, testosterone and cortisone levels of the participants.

Later, 94 Latvian women of the same age were asked to rate photos of each man on a 10-point scale of attractiveness, and the researchers then looked for links between the immune response as measured by hepatitis B antibodies, hormone levels and attractiveness.

The results, published Tuesday in the journal Nature Communications, found men with the strongest immune responses were rated by the women as better looking than those with weak immune responses. They also found men with elevated stress hormone cortisol rated low among women, suggesting stress may be detrimental to health.

Moore explains the reason for this increase in attractiveness is because men with stronger immune systems also tend to have more testosterone, the male sex hormone. More testosterone usually means a hunkier man, which women are generally attracted to.

Bottom line: Macho men look healthier.

Since the study is the first to directly link how women feel about a man’s looks with the strength of his immune system, researchers will next see if that link holds up across various cultures and people of different ages.

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