They say eyes are the window to the soul. Your peepers may also offer a peek into your medical records. Thanks to evolution, people can instinctively decipher other's health by checking out their faces. But sometimes we use the wrong clues, according to research at Brandeis University.

Most people automatically assume pretty people are healthier, but the Brandeis researchers say they're wrong. In men, there's no link; and in women, the link is actually negative. Victor Luevano of Brandeis suggests it's because attractive women are more social and pick up more pathogens, though "that still needs to be tested."

Emotional expression seems to signal wellness, but in men it's an empty gesture. Women who are healthier smile more. (Maybe they're happy to be illness-free.) But in men, more testosterone means a stronger immune system—and a more stoic façade.

Why would we follow false leads?

According to Luevano, "Perhaps in our distant past, attractiveness was strongly linked to health. In more modern times this relationship has been weakened, but our responses have yet to change."

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