Google "does borax remove blood stains" and you'll get a whole bunch of info similar to this:
Homemade chemical cocktail. Borax + washing soda + Tide powder detergent in a 1:1:2 ratio (the recipe I use is 1/4 cup Borax, 1/4 cup washing soda, 1/2 cup Tide powder). Mix the whole thing in a bathtub full of the hottest water that can come out of the tap, then dump your sheets (or towels or other laundry, I guess) and let it sit there until the water is cooled. Stir it every so often with a broom handle to make sure everything gets even coverage and so that you can pretend to be a witch with a cauldron. Then you squeeze the water out and wash it in the washer with water only, no more detergent, and dry as normal.
The Borax and washing soda are detergent boosters: they make hard water soft and increase the effectiveness of detergent. It's very, very strong. If you watch videos on Youtube or TikTok of laundry stripping until the water is black, that's dye leaching out of the fabric. It is not for every day use; it's the nuclear option. I've only done it once per set of sheets I own, and I'm not going to do it again for at least another several months. I'm definitely not going to do it on my regular clothes.
But if you have extremely set-in stains that absolutely will not come out, and the fabric can take it, it makes it like new. I had a set of sheets that had yellow blobs in the shape of my fiancé and I where we sleep the most often, because our sweat and body oils and nighttime drool were seeping into the fabric, and OxyClean and repeated laundering did nothing. Stripping did.
https://www.reddit.com/r/CleaningTips/comments/nz66dt/laundry_stripping_removes_bloodstains_like_a_beast/Unlike other cleaners, borax has few "bad" reactions, but some metal salts will form insoluble borates.
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