|I have no idea, but it does eventually bleach out my black yoga pants (I go commando in them).|
Add me to the sisterhood...it's happened since I was a teenager.
I once lived with a then-boyfriend's parents, and she was EXTREMEMLY OCD, so she did all of the laundry to make sure it was done "right". Imagine my embarrassment when she took me aside and suggested I might want to wear pantyliners to stop discoloring my underwear...THE HORROR, OH MY THE HORROR!!!
I've heard it is caused by a high acid content, but I've never asked anyone about it. Just Google.