First few minutes
Just happened? Do this first
- Blot with a clean, dry white cloth. Don't rub.
- Rinse with cold water only, never hot.
- Pretest any cleaner on a hidden spot first.
- Act quickly, since fresh blood lifts much more easily.
Blood on siding is a protein stain, and hot water is what sets it, so cold water is the rule until the spot is gone. Vinyl, fiber cement and wood all take water, but abrasives and strong solvents need care, so let the surface decide how hard you scrub. A fresh stain rinses away far more easily than one that has dried, so don't wait on it.
When you're removing blood stains from siding, work from the top down so runoff doesn't leave streaks on the lower boards. Test a hidden spot first, especially on bare wood, where a wet scrub can raise the grain. If the mark is still there after a rinse, stop scrubbing and call a pro once the wood starts to fuzz or lift.
Before you start
What siding, roof & exterior can take
Safe to use2
- Water
- Oxygen bleach
Use with care5
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
7 items
What you'll need
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- Clean, dry white cloths or white paper towelsBlotting with white material lifts the blood without adding color to the siding. (opens Amazon)
- Garden hoseA low-pressure cold rinse carries loose blood off the surface.
- Mild liquid dish detergentIt makes the gentle scrub work on every siding type. (opens Amazon)
- Soft brush or clothSafe for vinyl and fiber cement. (opens Amazon)
- Stiff synthetic-bristle brushWorks along the grain on wood without leaving iron stains. (opens Amazon)
- 3% hydrogen peroxide from the drugstoreFor a faint mark left after rinsing, not the stronger hair-bleach solution. (opens Amazon)
- Oxygen-bleach deck cleanerOnly for a stubborn spot on bare wood. (opens Amazon)
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5 steps
Step by step
Step 1 of 5
Blot up the fresh blood
Press a clean, dry white cloth or white paper towel onto the blood and lift it, then move to a fresh section and repeat. Work quickly, because fresh blood comes out much more easily than blood that has been sitting for more than 24 hours.
Careful. Rubbing spreads the blood and can damage the surface.
Step 2 of 5
Rinse with cold water
Spray the spot with cold water from a garden hose on low pressure, keeping the water moving across the stain rather than blasting it. Keep rinsing until the red or pink tint no longer runs off the siding.
Careful. Hot water sets blood into the surface, so keep it out of the rinse.
Step 3 of 5
Pretest on a hidden spot
Try the mild dish detergent and any pressure washer setting on a hidden spot, such as the underside of a board or a corner that is out of view. Check the spot once it dries and look for any color transfer or change. If you see a change, stop and choose a gentler option.
Step 4 of 5
Scrub gently with mild soap
Mix mild liquid dish detergent with water and work it over the spot with a soft brush or cloth on vinyl and fiber cement. On wood, use a stiff synthetic-bristle brush and always scrub along the grain. Keep your scrubbing light, and let the soapy water do most of the work.
Careful. Steel wool and wire brushes leave iron that stains wood.
Step 5 of 5
Rinse everything away
Rinse the whole area thoroughly with the hose so no soap is left on the siding. Look at the spot in daylight once it dries. If a faint mark is left, use the set-in treatment below rather than scrubbing harder.
If you'd rather buy than mix
Best products for blood on siding, roof & exterior
Look for mild liquid dish detergent for the scrub, and keep a few clean microfiber cloths close by. A soft brush suits vinyl and fiber cement, while a stiff synthetic-bristle brush suits wood.
Amazon Basics Microfiber Cleaning Cloths
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on siding, roof & exterior, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
If the stain was already dried or set, the method changes.
Old, dried or set-in stains →When to call a professional →How to tell it's working
The spot should look lighter after each cold rinse, and the rinse water should run clear of red or pink. If the color darkens, spreads or the surface starts to look different, stop and check your pretest results before going on.
What changes for yours
Adjust for your siding, roof & exterior
Vinyl siding
Vinyl gets the same cold rinse and gentle scrub, but it is sensitive to solvents. Skip undiluted bleach, liquid grease remover, nail polish remover and furniture polish, and use a soft brush or cloth.
Keep any pressure washer spray low and angled downward, and never aim it upward under the panels. For fresh blood, a light scrub and a quick rinse are the whole job.
Fiber cement siding
Fiber cement takes the same cold rinse, but use low-pressure hose spray rather than a power washer. Scrub with a soft brush or cloth, and leave out bleach and abrasive sponges, which can damage the finish.
For mildew, use a mildew-specific cleaner on a soft cloth. Rinse it away thoroughly, so no soap or cleaner is left drying on the surface.
Bare wood siding
Bare wood takes the cold rinse and the scrub along the grain well, as long as the spray is kept low and fan-shaped. Use the lowest pressure that cleans, and always spray with the grain.
Soft woods such as western redcedar need a gentle hand, since aggressive scrubbing or caustic cleaners can remove wood from the surface. If a stubborn spot stays, use the oxygen cleaner treatment described below, which is only for bare wood like this.
Painted wood siding
Painted wood gets the same cold rinse, mild dish detergent and light scrub. Skip the oxygen-bleach deck cleaner, since it is not safe on painted surfaces, so the rinse and scrub are your full treatment.
Test any pressure washer setting in an inconspicuous area before using it on painted boards, and keep the spray along the grain.
Rust or tannin streaks on wood
Reddish-brown tannin bleed or rust streaks from nails need a different product than soap and water. Use an oxalic-acid wood brightener and follow its label directions exactly. It also neutralizes oxygen cleaners, so rinse any oxygen cleaner away before you start.
Do not use acid on fiber cement siding, so check the material before you open the bottle. Rinse the brightener off thoroughly with the hose once the streak has faded.
Old, dried or set-in stains
Old blood that has been on siding for more than a day is harder to lift, so always start with the cold rinse and gentle scrub before trying anything stronger. Set-in treatments are only for what remains after those steps.
Dried blood needs patience more than force. On bare wood, keep an oxygen-bleach deck cleaner wet on the spot for about 15 minutes, misting it with the hose if it dries out, then scrub along the grain and rinse it away.
If a faint mark is still there, dab 3% hydrogen peroxide from the drugstore on it, then rinse it off. Test a hidden spot first and stop if the color changes. Some siding keeps a faint shadow after the best effort, so accept that rather than pushing harder.
Vinegar, baking soda, peroxide and more
Do home remedies work on blood on siding, roof & exterior?
Most home remedies either do nothing for blood on siding or make it worse. The method above uses only cold water, mild dish detergent and a careful rinse, with 3% peroxide and an oxygen cleaner as the set-in options.
Works1Helps2Skip3
Chemical safety
Never mix these
Some products in this guide react dangerously with each other. Use them one at a time and rinse with water in between.
Hydrogen peroxide (3%) + Oxygen bleach (OxiClean)
OxiClean's maker says it should not be mixed with household chemicals other than detergent in the wash.
If they mix by accident: Don't use the mixture; ventilate the room and avoid breathing fumes or touching it; call Poison Control at 1-800-222-1222 for disposal advice or if anyone feels unwell.
What makes it worse
Mistakes to avoid
Don't mix cleaners
Never combine bleach with ammonia, vinegar, other acids or rubbing alcohol. Rinse each product out with plain water before you move to the next one, since mixed products can give off toxic fumes.
Don't let soap dry on the siding
Never let cleaner or soap dry on the surface, so rinse each section as soon as you have scrubbed it. Work in small sections so the rinse can keep up with the scrub.
Don't scrub harder when a mark lingers
Repeated hard scrubbing wears down the finish before the stain is gone. Move to the set-in treatment instead, and stop if the spot changes color or starts to look worn.
When to call a professional
If a mark survives the cold rinse, the scrub and the set-in treatment, stop before you go harder. A pressure washer can damage siding in the wrong hands, so a siding professional is the safer call for stubborn wood or fiber cement.
Questions
How long can blood stay on siding before it's hard to remove?
Fresh blood comes off much more easily than blood that has been on the siding for more than 24 hours. Older stains still respond to the cold rinse and gentle scrub, so start there before you move to the set-in treatment.
Can I use vinegar to clean blood off siding?
No. Acid can make protein stains harder to remove, so start with cold water and mild dish detergent, rinse well with the hose, and use the set-in treatment only if a faint mark remains. Stick with cold water and mild dish detergent, rinse the spot thoroughly with the hose, and move to the set-in treatment only if a faint mark is left behind.
Is bleach safe on vinyl siding?
Undiluted bleach should stay off vinyl, along with solvents like nail polish remover. For vinyl, stick with the cold rinse and a soft brush.
Can hydrogen peroxide lift a faint blood mark?
It can help with a faint mark that remains after rinsing. Use the 3% drugstore antiseptic, test a hidden spot first, and rinse it off afterward.
Is it safe to scrub fiber cement siding?
Yes, with a soft brush or cloth and mild dish detergent in water. Avoid hard metal brushes and abrasive sponges, which can damage the finish.
What if my wood siding has turned gray?
Weathered wood can be restored with a commercial deck cleaner, brightener or restorer, which removes dirt and mildew so the wood's own color shows. If all natural color has leached out, the wood stays silver when dry and should be left as it is.
Blood on other materials
Other stains on siding, roof & exterior
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.