The short answer: don’t use hydrogen peroxide or iodine cleansers on a pressure sore unless your provider tells you to, because they can damage the skin.
Here’s what to use instead. For a stage I sore, wash the area gently with mild soap and water. For a stage II sore, clean the area with salt water, also called saline, and rinse to remove loose, dead tissue.
The words “unless your provider tells you to” matter, and it helps to see what that looks like in practice. After cleft lip and palate repair, a child’s surgeon may give you a special liquid, hydrogen peroxide, for cleaning the wound, applied with a cotton swab. If the surgeon has not, you clean with warm water and soap instead.
Those two instructions don’t contradict each other. Together they show hydrogen peroxide as something a clinician may choose for a particular wound, not a general-purpose antiseptic to reach for at home.
This is guidance written for particular wounds: pressure sores, and one specific surgical repair. It is not a universal rule, and instructions given for your own wound come first.