Do you find yourself forgetting things more often when you have your period? Despite scientific evidence to the contrary, some women still complain of ‘brain fog’ while menstruating, and for them it all seems too real.

Back in the 1990s, research into the relationship between hormones and brain function was first linked, with Swedish scientists making a connection between estrogen and the areas of the brain that manage memory and attention. This made them think there may be a link between fluctuating hormone levels and brain fog. Other studies suggested it might even affect spatial awareness and verbal fluency.

The trouble with the science, however, was it wasn’t consistent. While some experts concluded a higher level of estrogen led to poor cognitive performance, others showed that it actually improved clarity. (Put simply, it’s complicated.)

Unlike baby brain, which scientists agree is an actual phenomenon (even if they aren’t clear on what causes it), period brain has been pretty comprehensively debunked in recent years, after a comprehensive 2017 study of Swiss women – who were subjected to a battery of cognitive tests at various stages of their cycles – found that the menstrual cycle had absolutely no effect of the results. Yep, zip.

Over and out? Um, not quite. Seeing as there are still women with mild to moderate symptoms, the myth persists. It’s thought that it may be because declining estrogen and progesterone levels a day or two before your period affect your sleep quality, and it’s actually the sleep deprivation that causes the fog. You can read more about that here.