Everyone should know how to wash period stains.
Pre-rinse with cold water in the sink or tub.
Warm water will make it ‘clot’ and set in.
Put a moderate amount of table salt on stained area.
Gently rub into the fabric. You want a paste-like amount, not seasoning.
Let sit in for 15-30 minutes.
The longer you let it sit, the more salt you use, the more the fabric will fade/thin. It’s a balance, but I always err on the side of stronger treatment. A bit of color fading is usually better than a stain.
Rinse out salt thoroughly with cold water.
You shouldn’t need an abrasive, but a soft, clean kitchen sponge can be used if there’s still dried blood or embedded salt.
If it’s delicate: hand wash with cold water and drip-dry.
Anything lacy, non-cotton or patterned is probably delicate. If you’re not sure, better to just hand wash. If you’re only cleaning one or two pairs of underwear, I just use the residue in the cap of of the detergent bottle; a little detergent goes a long way. DO NOT WRING DRY.
If it’s not delicate: machine wash ASAP on tap-cold.
This goes for sheets, pants or larger loads of cotton underwear. The sooner you get it in, the better chance you’ll have of getting the stain out and reduce color fading from leftover salt.
Inspect after washing, repeat if needed.
This especially goes checking before machine-drying on any temperature. True for almost any stains: once you dry with heat, that stain isn’t going to come out.
Screenshots via relationships.txt on Twitter.