Menstrual bloodstains on your panties, as well as other absorbent materials such as bed sheets are almost a given among menstruating women. You can eliminate many menstrual bloodstains by washing your panties out in cold water, immediately upon discovering the stain. Quickly wash menstrual bloodstains from larger items in your washing machine using the cold water cycle.
If you are unable to immediately wash out menstrual bloodstains from your panties, try keeping your bloodstained panties separate from your other panties and wear them only when you are on your period. That way you will not end up with menstrual bloodstains on all of your panties.