To remove a musty smell from a book, first air it out for one to two weeks in a cool room with good circulation and relative humidity between 35% and 55%. If the smell remains, seal the book in a container alongside — but never touching — an odor absorber like unscented clay kitty litter, activated charcoal, or baking soda for two to four weeks.
That's the whole answer. But it comes with a fork in the road that almost nobody online mentions, and taking the wrong branch is how people end up making a book worse.
Is it musty, or is it mold?
These are two different problems, and they want opposite things from you.
Musty is an odor. The book got damp at some point in its life — a basement, a garage, a house with one badly ventilated wall — and it has held onto the smell of that period like a grudge. The paper is dry now. Nothing is growing.
Moldy means something is, or recently was, alive on it. Look for fuzzy or powdery patches, a slightly furry texture, faint spidery staining, or a surface that looks damp. The Library of Congress uses a blunt test: active mold "looks wet or furry."
The distinction matters because sealing a book in a container is the standard fix for mustiness — and close to the worst thing you can do to a book with live mold, which needs dry air and low humidity to go dormant, not a sealed box.
Here is the honest verdict on every method you'll find recommended:
| Method | What it actually does | Verdict |
|---|---|---|
| Open-air circulation, cool room, 35–55% RH | Lets absorbed odor compounds dissipate. The Library of Congress specifically notes musty smells diminish when items are stored with air circulation and not enclosed | Start here. Always. |
| Sealed container + absorber (not touching the book) | The Northeast Document Conservation Center's own recommended method: baking soda, unscented clay kitty litter, charcoal briquettes without lighter fluid, or zeolites | Works. Slow — 2 to 4 weeks |
| Zeolite interleaving paper | Molecular traps placed between the pages; NEDCC calls these "very effective in removing odors" | Best result, costs money |
| Absorber sprinkled directly on the pages | Leaves residue in the gutter and on the paper. NEDCC's method deliberately keeps the absorber in a separate container | Skip |
| Freezing | Kills active mold and halts growth. NEDCC recommends it when material can't be treated within 48 hours | For mold, not for smell |
| Microwaving | Glue softens, any metallic ink arcs, and readers who have tried it report it left the book smelly and transferred the smell to the microwave | No |
| Direct sunlight | Fades boards and spines and accelerates paper embrittlement — you trade an odor for permanent damage | No |
| Dryer sheets, incense, perfumed inserts | Masks rather than absorbs. One reader stored books with incense packets and spent weeks afterward removing the incense | No |
Why do old books smell in the first place?
Worth separating two smells that get lumped together, because one of them is not a problem at all.
The warm vanilla-and-almond scent people genuinely love is the paper slowly falling apart. As lignin and cellulose break down through acid hydrolysis and oxidation, they release volatile compounds: vanillin (vanilla), benzaldehyde (almond), toluene and ethylbenzene (sweet), 2-ethyl hexanol (faintly floral), and furfural, which conservators use as a marker of a book's age and condition. That smell is chemistry, and it is doing you no harm.
Mustiness is something else: the signature of moisture and microbial activity, past or present. It doesn't develop on a book kept dry. It develops on a book that spent a winter somewhere it shouldn't have — which, if you buy secondhand, is most of them.
If you're the sort of person who has opinions about this — and if you've read this far, you are — you may recognize yourself in our booktrovert collection.
How do you actually get the smell out?
Step 1 — Air it out, properly, before anything else
Stand the book upright, fan the pages open, and leave it in a cool room with moving air for one to two weeks. Not a sunny windowsill. Not the garage it probably came from. A quiet corner with a door that opens.
Aim for relative humidity between 35% and 55% — the range the Library of Congress recommends for storage and mold prevention. A cheap hygrometer costs a few dollars and takes the guesswork out permanently.
For a lot of ordinary secondhand paperbacks, this alone is enough. It's also the step everyone skips, because it doesn't feel like doing something.
Step 2 — The chamber method, done the way conservators do it
Only if airing hasn't finished the job.
- Take a large sealable container — a clean bin or tub with a lid.
- Put your odor absorber in the bottom: baking soda, unscented clay kitty litter, charcoal briquettes without lighter fluid, or zeolites.
- Place the book inside a smaller open container, and set that inside the big one. The absorber must never touch the book.
- Close it. Leave it two to four weeks. Check weekly.
That third step is the one the internet gets wrong, and it's the difference between a deodorized book and a book with baking soda permanently in its gutter.
If you want the professional-grade version, zeolite-loaded interleaving paper placed between the pages works faster and better. It's the one paid upgrade actually worth it for a book you care about.
Step 3 — Accept that it's slow
Readers who report success describe three weeks, and often a second round. A book absorbed that smell over years. It does not give it back in a weekend.
What if it really is mold?
Change of plan, and take it seriously.
NEDCC's guidance for handling moldy material is unambiguous: disposable nitrile gloves, protective clothing, goggles, and an N95 or N100 mask. Their warning is worth repeating plainly — exposure to mold sensitizes you, and that sensitivity can become an allergy. This isn't a one-book risk; it's a cumulative one.
The sequence:
- Dry it out first. Mold spores go dormant below 70°F and below 60% relative humidity. You cannot clean active mold — you'd smear it.
- If you can't dry it within 48 hours, freeze it. NEDCC recommends freezing to kill active mold and halt growth when treatment has to wait. Freezing buys time; it is not a deodorizer.
- Clean it dry. A HEPA vacuum on its lowest setting, or a soft wide brush — a watercolor brush is ideal — to lift spores off the surface. Do it outdoors if you can.
- Fix the room. NEDCC notes that if the smell comes back after cleaning, the condition that caused the mold probably hasn't been repaired.
Know when to stop. A $3 thrift-store paperback with mold through the text block is not worth your respiratory system. Let it go and buy another copy. A book with real value goes to a conservator, not to a bin with kitty litter in it.
How do you stop it happening again?
The single most useful thing in NEDCC's guidance is also the least glamorous: attics and basements are not adequate storage. Not because they're dirty — because their temperature and humidity swing wildly, and books hate change more than they hate any particular condition.
The numbers that decide everything:
- Mold is likely at over 75% RH for a month at 70°F, at 80% RH for two weeks, or at 90% RH for four days
- On genuinely wet material, mold can appear in about 48 hours
- Spores stay dormant below 70°F and below 60% RH
- Target range for storage: 35–55% RH
Keep books in the lived-in part of the house, off exterior walls, not pressed flat against the back of a deep shelf where air can't move. That's it. That's the whole preventive program.
Which is a fine excuse to think about the shelf itself — and if you're building the reading corner to put it in, we wrote about the fall reading aesthetics people are actually chasing, and stocked our cozy and cottagecore collection accordingly.
Frequently asked questions
Is the musty smell in books dangerous?
An odor alone is not a hazard, but visible mold can be. NEDCC advises gloves, goggles and an N95 or N100 mask when handling moldy material, and warns that repeated exposure can sensitize you over time. If a book looks wet or furry rather than simply smelling stale, treat it as mold.
Does baking soda actually remove book odor?
Yes, in a sealed container — provided it never touches the book. NEDCC lists baking soda alongside charcoal, unscented clay kitty litter and zeolites as odor absorbers, with the book placed in a smaller open container inside the sealed one.
How long does it take to get the musty smell out of a book?
One to two weeks of open-air circulation for mild cases, and two to four weeks in a sealed chamber for stubborn ones. Readers who report success commonly need a second round. Nothing about this process is fast.
Can you put a book in the freezer to remove the smell?
Freezing kills active mold and stops it spreading, which is why NEDCC recommends it when material can't be treated within 48 hours. It does not remove odor. Use it as a mold emergency measure, not a deodorizing step.
Will sunlight get rid of the smell?
It will fade the boards and spine and make the paper brittle faster. Use a cool room with moving air instead — the Library of Congress specifically links reduced musty odor to air circulation, not to light or heat.
What humidity should books be stored at?
Between 35% and 55% relative humidity, per Library of Congress guidance. Mold becomes likely above 75% RH sustained for a month, above 80% for two weeks, or above 90% for four days.