How to get old blood stains out of a mattress?

Old blood stains come out of a mattress by working a cold paste of baking soda and hydrogen peroxide into the spot, letting it sit, then blotting and air-drying it fully.

Hot water cooks blood proteins into the mattress fabric, so cold is the rule. Mattress foam and coil layers also hold moisture, which is why a mattress stain treatment stays on the surface, uses blotting rather than rubbing, and dries completely before sheets go back on. Repeat the treatment for stains that have set for weeks.

Hot water sets blood stains on a mattress, so every step uses cold water.
Common mattress stain lifters are hydrogen peroxide, baking soda, and cold salt water.
Memory foam mattress layers absorb liquid slowly and dry slowly, so surface-only treatment matters.
Some mattress covers are non-removable, which limits stain treatment to the surface fabric.

01Step-by-Step

Strip the bed: Remove sheets, the mattress protector, and any topper so the stained mattress surface is fully exposed and nothing else gets splashed.
Mix the paste: Combine two tablespoons of baking soda, one tablespoon of cold water, and one tablespoon of 3% hydrogen peroxide until it forms a loose, spreadable paste.
Test a hidden spot: Dab a tiny amount on an unseen corner of the mattress cover, wait five minutes, and check that the fabric color holds before treating the stain.
Apply to the stain: Spread the paste over the dried blood with a spoon or soft cloth, covering the whole mark without soaking the fabric through to the foam.
Let it sit: Leave the paste on the stain for 30 minutes, longer for stains that have set for weeks, so the peroxide can break down the old blood proteins.
Blot it away: Press a clean cloth dampened with cold water onto the paste, lifting it off in small dabs instead of rubbing the stain deeper into the mattress.
Dry completely: Pat the area with a dry towel, then air-dry the mattress with a fan or open window before remaking the bed, repeating the treatment if a shadow remains.