Article: Usually, a solution with 3% strength would suffice.

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Lay out the Pillowcase on a work area. Pour hydrogen peroxide directly on the blood spot. Let the hydrogen peroxide fizz or bubble for a few minutes, to allow the chemical to react to the blood spot and break it down. Blot with a damp sponge or cloth. Repeat steps 2 to 4 until the blood spot is removed. Launder the Pillowcase as usual, in cold water.