Aside from fats being nasty just as a rule, period underwear are actually a great, environmentally sound choice. It's basically a sewn-in pad that's launderable instead of landfill waste, and isn't any more unhygienic than wearing a pad would be, since you don't... wear the same one all week. You have multiple that you throw in the wash and exchange for clean ones. Some women don't like tampons because inserting them is messy, and they can be really painful for some of us. Fats are disgusting, obviously. But absorbent menstrual underwear is pretty great. I use them to prevent leakage when cycling.