The brown bottle has been in medicine cabinets for a century. Cut yourself, pour it on, watch it foam. The foaming feels like proof.

The foaming is real. The cleaning is not, and the substance is actively working against the wound.

Hydrogen peroxide is a broad-spectrum oxidizing agent. It kills bacteria by tearing apart their cell membranes and oxidizing their proteins. That much is true and it is why it works as a disinfectant on a countertop.

The problem is that it does exactly the same thing to your cells.

The fibroblasts laying down new tissue, the keratinocytes resurfacing the skin, the new capillaries growing into the wound bed — peroxide destroys them without discriminating. The cells you need to close the wound are the cells being killed by the thing you are using to clean it. Multiple studies have found peroxide-treated wounds heal more slowly than wounds irrigated with plain saline or even tap water.

The foaming, incidentally, is not bacteria dying. It is catalase, an enzyme present in your own tissue and in blood, breaking hydrogen peroxide into water and oxygen. You get the same bubbles on a clean cut with no bacteria in it at all. The visual feedback everyone trusts is a reaction with you, not with the infection.

What actually cleans a wound is water and pressure.

Irrigation. A lot of clean water, moving fast enough to physically flush bacteria and debris out of the tissue. Saline is ideal. Clean tap water is fine and the evidence on that is good. A syringe gives you useful pressure; so does a plastic bag with a pinhole squeezed hard, or a squeeze bottle.

The mechanical force is doing the work. You are not chemically sterilizing anything — you are washing it out.

Then dry the area, cover it with a clean dressing, and leave it alone. Change the dressing daily and look for the signs that actually mean infection: expanding redness, red streaking away from the wound, increasing pain rather than decreasing, warmth, cloudy or foul drainage, fever.

Skip the alcohol too, for the same reason and with the added feature of being needlessly painful.

If the wound is deep, gaping, heavily contaminated, from a puncture or an animal bite, or if it is on a hand or a face, get it looked at. Tetanus status matters. Some wounds need closure within hours to close well.

The American College of Emergency Physicians and wound care specialists moved off routine peroxide years ago.

Rinse it with water. Dry it. Cover it. That is the whole protocol, and it is less satisfying than the foam.

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