Some people say they're 'allergic to their period.' Here's what to know about the autoimmune skin condition that causes it.

"Basically, your own immune system starts forming either an allergy or a sensitivity to progesterone. We have progesterone in our body as a hormone, and so normally, we shouldn't be allergic to it because it's a naturally occurring thing."

"What we know is there is a sensitivity or an allergy that seems to be a reaction to the high progesterone levels that occur during the luteal phase, which is directly before the menstrual period."

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