There’s a growing body of research showing that children exposed to lots of germs early in life are less likely to develop allergies, asthma or autoimmune disorders as they grow up. But now there’s a new twist on the theory, known as the hygiene hypothesis in scientific circles, and it’s about little girls in cute little dresses.

In an article in the peer-reviewed journal Social Science and Medicine, Sharyn Clough, a philosopher of science at Oregon State University who studies research bias, says young girls are held to a higher standard of cleanliness than young boys, a discrepancy that could help explain later health differences. Girls are expected to stay squeaky clean while boys are encouraged to play outside, Clough argues. And that might explain why women have higher rates of certain illnesses.

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