Book-Condition Library
A book has mold if you see fuzzy, powdery, or web-like growth (white, green, gray, or black), usually raised from the surface and accompanied by a strong musty smell, often starting at the edges, gutter, endpapers, and cover. Mold has texture, can smear, and spreads, which sets it apart from flat reddish foxing spots and from ordinary dust. Because mold releases spores that can irritate the lungs, move a moldy book away from your other books (a sealed bag is fine for the move, not for storage) and handle it in a ventilated area with an N95 respirator and gloves.
Published June 2026 · By Josh Eldred, New Mexico Literacy Project
Clearing a musty shelf? The clean books can go straight into my covered 24/7 drop box on Edith Blvd NE. Bag anything moldy separately and mention it when you text 505-250-3804 for a free metro pickup, so it rides apart from the clean donations.
What mold looks and smells like
Mold (and mildew, a common surface mold) shows up as fuzzy, powdery, cobwebby, or slightly slimy growth that sits on or in the paper and binding. It can be white, green, gray, black, or even pinkish, and it usually brings a strong musty odor. Check in good light along the most vulnerable spots: the page edges, the gutter (where pages meet the spine), the endpapers, and the inside of the covers. If a patch looks raised or furry and the book smells damp and sour, assume it's mold.
Mold vs. foxing vs. dust
Mold / mildew
Living growth — fuzzy, powdery, or slimy, with texture you can see and feel. Many colors, musty smell, and it spreads in humidity. Needs action.
Foxing
Flat, rusty-brown age spots with no texture; it doesn't grow or spread like an organism. A cosmetic age condition, not a contamination — see what is foxing.
Dust & dirt
Loose surface grime that brushes off cleanly, with no growth pattern and no musty smell. Handled with simple dry cleaning.
The quick test: texture and spread. Fuzzy/powdery and getting worse = mold. Flat and stable = foxing. Wipes away = dust.
Why it matters: health and spread
Two reasons to take mold seriously. First, health: mold releases spores that can trigger allergic reactions and respiratory irritation, and anyone with asthma, allergies, or a weakened immune system should not handle moldy books at all. Second, cross-contamination: spores travel, so one moldy book shelved against clean ones can spread the problem through a collection. Treat a moldy book as something to isolate, not to slot back on the shelf.
How to handle a moldy book
1. Isolate it
Move it away from your other books. A sealed plastic bag keeps spores from spreading on the way, but take the book out once it's in a dry, separate spot: NEDCC warns that a book left sealed in plastic sits in its own damp pocket of air, which can feed more growth.
2. Dry it out
Mold needs moisture; lowering humidity halts active growth. Aim for a room below 55 percent relative humidity and under 70°F, the target NEDCC gives for stopping mold. New Mexico's dry air helps, but get the book out of any damp space first. (If it's actually wet, see water-damaged books.)
3. Brush off the dormant mold outdoors
Once it's dry, mold goes dormant and turns powdery. Brush that residue off gently outdoors, wearing an N95 respirator and gloves, never indoors, where you'd just scatter spores into the room. Brush away from yourself and don't rub, which grinds mold into the paper. Dormant isn't dead: the spores can wake up if the book gets damp again.
4. Call a conservator for valuable or heavy cases
Significant mold, or a book that may be valuable, is a job for a professional conservator rather than home treatment. NEDCC advises leaving active (soft, fuzzy) mold to a conservator entirely; the full cleaning steps for dry, dormant mold are in my book cleaning and repair guide.
Frequently asked questions
What does book mold look like?
Book mold usually looks like fuzzy, powdery or cobweb-like growth that sits slightly raised on the paper or binding. It can be white, gray, green, black, or occasionally pink or orange, and it tends to start at the page edges, the gutter near the spine, the endpapers and the inside of the covers. A sour, musty smell almost always comes with it.
What does mold on book pages look like?
On the pages themselves, mold shows up as dusty or fuzzy patches, clusters of small dark dots, or soft blotches, often along the edges or where pages touch. Pages may also be stained, stuck together or cockled from the moisture that let the mold grow. If a spot smears or lifts when brushed, it's likely mold rather than foxing.
How can you tell if a book has mold?
Look in good light for growth with texture (fuzzy, powdery or web-like) and smell the book. Mold has texture, can smear, and spreads in humidity. Flat rust-colored spots that don't change are foxing, and grime that wipes away cleanly is just dust.
Is it mold or foxing?
Foxing is flat, dry, rust-colored spotting that sits in the paper and doesn't spread. Mold is fuzzy or powdery, often musty-smelling, and grows in humidity. Foxing needs no quarantine; mold does. More on the difference in what foxing is.
What's the difference between mold and mildew on books?
Mildew is simply a common, flat surface mold that tends to look white or gray and powdery. Other molds grow deeper and fuzzier, in green, black or other colors. For a book the handling is the same: isolate it, dry it, and brush it outdoors once dry.
Does a musty smell mean a book has mold?
Not always, but take it as a warning. Aging paper gives off its own sweet, slightly sharp smell, and a book can stay musty long after old mold has gone dormant. A damp, earthy smell, especially with spots, stains or stuck pages, usually means mold now or in the past. Check the gutters and endpapers in good light; if you find no growth, a closed box with an open dish of charcoal or baking soda can take the smell down. More on that in how to get rid of musty book smell.
Is a white film on a leather book mold?
Not necessarily. Leather that was oiled or dressed years ago can bloom with a whitish, waxy or crystalline film called spew, as fats from the dressing work back to the surface. Spew tends to look smooth or speckled rather than fuzzy and doesn't smell musty, while mold looks furry or powdery and smells damp. If you can't tell, treat it as mold: wear gloves and keep the book away from others.
Is mold on books dangerous?
The spores can trigger allergic and respiratory reactions, so anyone with asthma, allergies or a weakened immune system should avoid handling moldy books. Work outdoors or in a ventilated space with an N95 respirator (a paper dust mask isn't enough) and gloves, and keep moldy books away from clean ones.
Can mold spread from one book to others?
Yes. Spores travel through the air and by contact, so a moldy book shelved against clean ones can spread the problem, especially in a damp room. Keep a moldy book apart until it's dealt with: bag it to move it, then let it dry out of the bag somewhere separate.
Can you save a moldy book?
Often, if the mold is light. Dry the book completely so the mold goes dormant, then brush the powdery residue off outdoors while wearing an N95 respirator and gloves. Heavy growth, a book that stayed wet, or a book that matters a great deal is a job for a paper conservator.
Should I throw away moldy books?
Only when the growth is heavy or the book is soaked through. Lightly affected books can often be dried and cleaned. If you're in the Albuquerque metro and would rather not deal with it, bag the moldy ones separately and text me for a free pickup. I sort what's salvageable and recycle whatever paper is clean enough to recycle.
Cite This Guide
Eldred, J. (June 2026). How to Tell If a Book Has Mold. New Mexico Literacy Project.
https://newmexicoliteracyproject.org/how-to-tell-if-a-book-has-mold
Licensed under CC BY 4.0.