Does Hydrogen Peroxide Kill Mold? How to Use 3% Safely

Does hydrogen peroxide kill mold? Yes, a 3 percent household solution can kill and lift surface mold on many hard materials such as tile, glass and sealed counters, and it is gentler on skin than bleach. It can lighten fabrics and paint, it does not reach deep into porous materials, and the mold returns if the moisture stays.

Does hydrogen peroxide kill mold: how it works

Hydrogen peroxide releases oxygen as it breaks down, which helps lift and kill mold on the surface. Standard drugstore peroxide is 3 percent. It is a common choice on bathroom tile, grout and sealed surfaces and is considered easier on the nose than bleach. As with vinegar and bleach, it works on the surface, not on mold rooted in drywall or wood.

Quick facts: does hydrogen peroxide kill mold
Strength	3 percent household solution
Contact time	About ten minutes, then scrub and wipe
Best on	Hard, non-porous surfaces and some sealed grout
Watch out	It can bleach fabrics, carpets and painted or stained surfaces

How to use it

1. Ventilate and protect. Wear gloves, goggles and a mask. Open a window.
2. Test a hidden spot first, because peroxide can lighten colors.
3. Spray the 3 percent solution directly on the mold in its original dark bottle or a dark spray bottle. Light breaks it down.
4. Wait about ten minutes.
5. Scrub with a stiff brush or sponge.
6. Wipe with a damp cloth and dry the area completely.
7. Repeat on stubborn patches, and dispose of rags.

Where it works

Surface	Result
Glass, tile, glazed ceramic	Works well
Sealed grout	Can work on light growth
Fiberglass tubs and sinks	Works
Painted drywall	Light surface growth only; test for color change
Raw drywall, ceiling tile, insulation	Replace; peroxide does not fix it
Fabrics and carpet	May bleach; follow garment care for laundry

What never to mix it with

Do not mix hydrogen peroxide with vinegar in the same container, because they form peracetic acid, which is corrosive and can irritate eyes and lungs. If you use both, use them one after the other, rinsing in between, and never store a mix. Do not mix peroxide with bleach, or with ammonia or other cleaners.

Safety

Keep peroxide in its dark bottle, away from heat and light. Avoid skin and eye contact and rinse with water if it splashes. Do not use higher strengths such as 35 percent food grade, which can burn skin and is dangerous. Keep children and pets away while you work.

Peroxide, vinegar or bleach?

Peroxide and vinegar are both good for hard surfaces and gentler than bleach. Peroxide may lighten colors, while vinegar can etch natural stone. Bleach is harsher and has the most hazards. Any of them is only as good as the drying and moisture control that follows.

Fix the moisture

Repair leaks, use fans, lower humidity and dry wet materials quickly. Without that, the mold you cleaned will be back.

Peroxide on grout and caulk

For grout lines, spray the peroxide, wait ten minutes and scrub with a small stiff brush. For stubborn stains, mix a paste of baking soda and peroxide, press it into the grout, wait fifteen minutes and scrub. Silicone caulk with surface mold may wipe clean, but caulk that is black all the way through should be cut out and replaced, since mold has grown into it.

Storage and shelf life

Hydrogen peroxide breaks down with light, heat and time, so keep it in its dark bottle in a cool cupboard and check the date. A bottle that no longer fizzes on a cut or a surface may be too weak to help. Do not pour leftover solution back into the bottle, because contamination speeds up its breakdown.

Tips for better results

Clean off soap scum and dirt first, because peroxide works best on a clean surface. Work in small sections so the surface stays wet for the full ten minutes. Dry everything afterward, since peroxide does not stop mold from growing back on a damp surface.

When to call a professional

If mold covers more than about 10 square feet, is inside walls, follows flooding or sewage, or returns after cleaning, call a remediation company. Asking does hydrogen peroxide kill mold is sensible for a small patch, but big problems need an expert plan.

Related reading

• Does Vinegar Kill Mold? What It Can and Cannot Do
• Does Bleach Kill Mold? Why It Often Fails and What Works
• Black Mold vs Mildew: How to Tell Them Apart and What to Do
• Mold After Water Damage: How Fast It Grows and What to Do

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