Autoimmune diseases, where the body’s own immune system mistakenly goes on the attack, are much more common in women – and a new study analyzing more than 1.25 million blood cells goes a long way to explaining why.

The analysis, led by a team from the Garvan Institute of Medical Research in Australia, revealed over 1,000 genetic ‘switches’ in immune cells that work differently depending on sex.

In short, these variations in gene activity mean that inflammatory pathways that respond to threats are likely to be busier in women, leading to a greater risk of conditions like lupus and multiple sclerosis.