Stains and costumes go together like peanut butter and chaos — but I've learned a few tricks that actually rescue my favorite shirts every time.
First, treat the stain fast. Scrape off any excess fake blood with a dull knife or the edge of a credit card, then blot (don't rub) with a white cloth or paper towel to lift as much as you can. Rinse the back of the fabric with cold running water to flush the stain out of the fibers; cold helps keep dyes from setting. If the fake blood is syrupy (lots of corn syrup or glycerin), pre-treat with a drop of grease-cutting dish soap worked gently into the stain with your fingertips or a soft toothbrush. Let that sit for 10–15 minutes, then rinse.
If the stain persists, I reach for an enzyme laundry detergent or an oxygen-based bleach (like sodium percarbonate products). Soak the garment in cool water with the product for several hours — overnight for stubborn dye stains — then launder on a cold cycle. For delicate fabrics I dilute a mild detergent and dab carefully, or take the piece to a cleaner if the label says dry clean only. For whites, a tiny dab of 3% hydrogen peroxide can help break down colored dyes, but always spot-test and blot immediately; hydrogen peroxide bubbles and can lighten fabrics unevenly. Never put a stained item in the dryer until the stain is gone: heat sets dyes permanently. I’ve saved costume pieces and tees this way more times than I can count, and it still feels like a little victory every time I get a stubborn blot out.