Moldy books (C) Daniel FriedmanMold Contamination on or in Books, Paper, Photographs
how to remove mold & mold stains and foxing from books & papers

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Mold contamination on or in books:

This article explains how to deal with mold on books and papers, and what options we have for cleaning or storing moldy books. The moldy books in a college library (photo above) were in the opinion of some people "an old inactive mold problem" but see our warning below about "dormant mold".

The extensive range and area of moldy books in this library was capable of producing very high (and unsafe) levels of harmful mold spores.

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Moldy Books and Papers - Can I Save Moldy Books?

Moldy books (C) Daniel FriedmanQuestion: Is it possible to get rid of mold in books?

I have mold disease and I'm wondering if it's at all possible to get rid of mold in books or if I need to give them all away. Should I even try? - E.A.

[Click to enlarge any image]

Article Contents


OPINION: A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem, so it could be dangerous to assume that the moldy books are the only or even the most serious mold problem in your home.

Watch out: as you indicate that you personally have a mold-related illness, you should not attempt a mold cleanup project yourself without first checking with your doctor. Most likely the physician will tell you to keep your hands off of mold stuff, and to have a professional handle the cleanup (negative air, dust control, containment, etc).



As we explain at MOLD AGE, HOW OLD is the MOLD?, especially in older buildings where there has been a recent sudden leak event associated with mold growth, it is often possible to identify pre-existing mold as well as mold-producing conditions.

Considerations When Preparing to Clean or Salvage Moldy Books or Papers

That said, here are some things to consider when deciding to clean or scrap moldy books or papers:

Moldy books (C) Daniel Friedman

So ultimately, if the books are valuable, some of them may merit professional cleaning. Otherwise, unless the mold on your books is superficial, it's more likely less costly to dispose of the moldy books and purchase new clean dry copies.

Dormant book or paper mold problems?

We have also read book mold cleaning articles recommending that you make the mold go "dormant" so that it's dry and powdery.

That makes some sense insofar as it's easier to vacuum or wipe off a dry powdery substance than damp moldy surfaces. And while we wouldn't call it a "dormant" state, the ongoing growth of mold may slow or even stop if conditions are no longer favorable for the particular species present - for example, if the books are dried and kept at sufficiently low humidity. But be sure to see our health hazard warning immediately below.

Health Hazards of Moldy Book Collections: Clouds of Mold Rose from the Library Book Shelves

Moldy books (C) Daniel Friedman

Watch out: The moldy books in a library (photo at page top and at left) were in the opinion of some of the parties "an old inactive mold problem".

But when workers began dehumidifying the area in preparation for a mold cleanup, conditions actually got quite dangerous: there were so many moldy books with such thick mold growth that visible clouds of Aspergillus sp. spores were released into the air by small air currents caused by simply walking down the aisle between stacks of books.

On book bindings we found heavy growths of Aspergillus sp. and on some books, Cladosporium sp. Not surprisingly, mold growth density varied significantly from book to book, even among adjacent books, depending on the binding materials.

Lab Photos of Book Mold from a Library

Our book mold lab photographs made from samples at the project above show dense Aspergillus sp. spores from a book binding surface (second photo below) and Cladosporium sp. fungal spores (below right) from a different book binding. Very high levels of airborne Aspergillus sp. were found in the book storage area after the dehumidifiers began operating and before the cleanup had begun.

Aspergillus on moldy books (C) Daniel Friedman

Below: Cladosporium spores and hyphal fragments:

Cladosporium sp on moldy books (C) Daniel Friedman

Properties of Typical Library Bookshelf Dust

By contrast, our lab samples and photos of typical dust found on bookshelves in areas of a library that were not mold-contaminated were more like typical house dust.

The dominant library dust particles were paper fibers, carpet fibers, skin cells and of course a few pollen grains and isolated fungal spores. In our photo of typical library bookshelf dust (below left) that large particle is pine pollen. In older sections of a library and in basements, insect fragments and elevated levels of dust mite fecals.

Typical library bookshelf dust (C) Daniel Friedman

Is there Ever Mildew on Books? 


Continuing from the comments on mold and mildew, where renovations had gone on nearby in the building, we found non-fungal granular debris typical of plaster or drywall dust (photo below right).

Typical library bookshelf dust (C) Daniel Friedman

We have seen several articles that refer to mildew on books. Those writers are almost certainly technically mistaken. Mildew (a much smaller subclass of members of the mold family) is an obligate parasite that grows on living plants - like grapes.

So unless your books are bound in grape leaves, the fungal growth found on books and papers is indeed mold, often Aspergillus sp. (especially on bindings) or other problem molds, but it's not actually mildew (Oidium-Erysiphe - powdery mildew, or Peronosporaceae - downy mildew).

Causes of Foxing or Rust Stains in Books or on Paper

Question/Comment: what causes rusty stains or foxing marks on books and paper ? Foxing definition, chemistry, causes, treatments or removal methods, and prevention

Foxing marks on paper edges and book pages in Hypatia by Dora Russell ca 1925 (C) Daniel Friedman

Are foxing marks on books and paper always caused by mould or are other factors also at work? Also, I have a couple of books with shiny pages that have become sticky during a humid summer and have developed orange lines along the edges of some of the pages.

Is this a reaction of the acid in the books seeping through the cut edges or could mould be a factor? - Rachel 9/2/202

Reply: iron oxide, fungi and yeast associated with foxing on books and papers: causes, cures, prevention


Your surmise that more than mold is at work in the development of local discoloration or reddish-brown foxing marks on paper and books is correct in that at the core, foxing is caused by exposure of those materials to high humidity, and the brown stains characteristic of foxing marks are typically found to contain high levels of iron oxide (FeO) in one or more chemical forms.

Paper chemistry as well as chemistry of inks and other materials comprising the book, paper, stamp, or other foxed document are also important components in the foxing problem. (Carter explains that the general yellowing of some paper products is distinct from the localized red-brown stains associated with foxing. [36][37])

Please see our detailed article that includes a more complete answer to your question, found at Details about foxing are at FOXING STAINS on BOOKS & PAPERS.

Watch out: Tronson warns

There has been no definite cure for neutralising the mildew [properly, mold not mildew - Ed] spore, chemical use not only breaks down the paper cellulose but also reactivates the ink so not only do the fibres of the paper break down, after a while and the paper starts to disintegrate and the ink or what ever medium can be rubbed off!
Bleach treated or chemical treated papers on the other hand will always be subject to the foxing returning and eventual disintegration. [25]

Question/Comment: distinction between "mold" and "mildew" is questioned

Moldy books (C) Daniel Friedman

As a book collector and once-upon-a-time mycologist I found your web site of interest.

However, I do not believe there would be uniform acceptance among professional mycologists of your distinction between "mold" and "mildew". The organisms involved are all fungi in the classical sense. Those attacking dead organic matter like cellulose are not all that different biologically from their relatives that may have a preference for the living cells of plants and animals.

The fact that some parasitic species may be facultative heterotrophs (feeding on non-living materials) supports this view.

I believe your cause is best served by promoting the idea that the fungi, a diverse and highly successful breed, will exploit any environment where nutrients and moisture are available whether or not it is living or dead. Books and their bindings in a high humidity environment are sitting ducks.

One final point: since fungi and their spores and hyphae are ubiquitous in nature it should be recognized that there is little chance of getting rid of all of them by any practical means (HEPA filters included). Since fungi (including species that attack damp books) play such an important part in our ecosystem we would be unwise to eliminate them entirely. We can, however, slow them down. - Chris 9/7/2012

Reply: Mildew doesn't grow on books, nor on leather shoes, nor on wallpaper, nor on other indoor building surfaces, though lots of other mold genera/species might


Thank you for the interesting comments about book mold, mildew, HEPA vacuuming, and the important role of the fungi in our environment. I'm grateful to read your opinion and want to emphasize that we welcome polite, informed discussion or debate about this or any other topic found at

Indeed even among expert book restorers the term mildew is often used loosely and technically incorrectly to refer to the role of certain fungi or mold genera/species in the cause of foxing on books and papers. A few points need clarification: by no means do I suggest that mildew is not a fungus, as mildew is indeed a proper subset of the huge kingdom of fungi. But the fungi appearing on books are different genera/species from the two fungi properly named mildew. There are some important distinctions to be made.

Mildew doesn't grow on shoes, nor on paper, though many other mold genera/species can grow on these materials

I learned about the distinctive properties of mildew as a living plant pathogen among other members of the Fifth Kingdom from Dr. John Haines, my friend and mentor, when John was still serving as the NY State mycologist. Discussing some mold samples I'd brought along for us to examine, I mentioned that I'd just collected some white mildew from leather shoes found in a moldy home. Like many people I just bandied the word mildew about willy-nilly. John asked why I thought it might be mildew, allowed me to embarrass myself, and then kindly explained that mildew grows on plants, not shoes.

Perhaps it's technical nitpicking, but mildew a subset of "mold" that only grows on living plants. Mildews are a small group of fungi found among the Basidiomycota, Ustilaginales if I recall correctly, and any "mildew" if properly identified, will be either Oidium-Erysiphe or Powdery Mildew or Peronosporaceae or Downy Mildew. Mildew, then, has nothing to do with and won't be found growing on books nor on other building surfaces unless the item in the building is a live or recently-live plant.

The fungi identified as growing on or in paper materials included the following

In research on foxing stains (see FOXING STAINS on BOOKS & PAPERS. ) experts have identified at least ten species of fungi and one yeast have been identified as growing on/in or "hosted by" paper, [16][17][17a][29]

In addition, when we add consideration of the different (from paper) materials used in book bindings, covers, etc., it is likely that there are additional mold genera/species that may be found growing on books. In our own field and lab experience, while there was some variation in mold genera/species present, the dominant fungus contamination found on the exterior of books in a moldy library basement was Aspergillus sp.

Indeed, a literature search confirms that among scholarly and research papers we researched for this article, not one authority detected the presence of either of the two types of mildew (Oidium-Erysiphe - powdery mildew, or Peronosporaceae - downy mildew) among the various fungi found growing on books, papers, photographs, stamps, or other paper based works. [1] op. seq. Fungal species commonly identified as found growing on or in books, papers, photographs, stamps, etc. include:

The fungi identified as mildew include these two groups

Below I include photos of Oidium or powdery mildew that I collected from a jasmine plant (below left) that was growing indoors (we moved it outside before this photo was taken) along with a photo of the same mildew from that plant under my lab microscope (below right).

Typical library bookshelf dust (C) Daniel Friedman

Below: microscipic view of mildew spores of Oidium:

Typical library bookshelf dust (C) Daniel Friedman

What's wrong with misidentifying fungi types or genera/species

You make an important point, that fungi are very versatile and that many genera/species adapt well to growing on stuff found indoors, including books. On the other hand, if my "mold expert" insists on calling white or light colored molds on books or on other indoor building surfaces "mildew" it makes me nervous on several scores:

Why does the Mold / Mildew Distinction Matter? Implications for Building Testing

Very moldy home (C) Daniel FriedmanFrom one point of view, since the remedy for an indoor (or book) mold problem does not depend much on the mold genera or species, understanding mycology might not seem to make much difference in improving a moldy indoor building area.

But that's not quite so. Having the luxury of my own forensic lab along with performing field investigations for many years, I have been able to make a wide study of which mold genera/species seem to best like different indoor building surfaces and materials.

I've enjoyed collecting mold samples from every single type of surface and material in very moldy homes, having cataloged (MOLD GROWTH on SURFACES, TABLE OF)
and photographed quite a few, nearly 100 of which can be seen online

This work has suggested that when building investigators or "mold experts" survey a building for mold contamination, a lot depends on where and how the sample is collected.

For example, in pulling a tape sample of mold growth on a hollow-core luan door in a very moldy home we find completely different genera/species preferring the edge of the door (probably southern yellow pine wood) from that growing on the door surfaces (luan mahogany). If the investigator does not realize this, his/her report that claims to characterize what molds are present or potentially harmful in the building might be quite inaccurate.

Watch out: In a library of moldy books, if by careless language we informed building management that we thought the dominant mold present was just a bit of mildew (say Oidium) we would erroneously conclude that other than a possible allergic response or perhaps a problem for nearby houseplants, there was no health risk to building occupants.

But in point of fact what I find on moldy library books is typically a potpourri of fungi dominated on book jackets by several species of Aspergillus - far more likely to present an IAQ and health hazard to occupants.

HEPA Vacuuming is Not a Mold Cure: the two key steps are remove the mold and fix the cause of mold growth

You are of course also completely correct that HEPA filtering of air is never a cure for mold problems on books or other indoor surfaces. Such cleaning is, however, an important step in mold remediation in general and in the cleaning of visibly moldy books and papers - a topic which we discuss in greater detail at Considerations When Preparing to Clean or Salvage Moldy Books or Papers. The effective cure for indoor mold problems involves two basic efforts:

  1. Remove the problem mold - this means physically cleaning it off (some remaining stains may be harmless)
  2. Find and fix the cause of high indoor moisture or leaks that caused the mold growth and fix those conditions

The reference to HEPA filtration that you may come across in reading about mold remediation in buildings typically involves either a HEPA filter on a machine used to create negative air pressure in the infected area in order to protect other building areas from cross contamination during the period of mold cleanup and repair work, or a HEPA filter used during dust cleaning in other building areas as a means of reducing indoor dust levels without just stirring up worse dust than before.

Why We Need Mold in the Environment

I also agree with and appreciate your observation that the fungi are a crucial part of our ecosystem - without them and their ability to break down cellulose (not just books, but leaves and dead wood) I doubt that their partner in cellulose decay (some bacteria) would alone be up to the job. Imagine the earth being buried in all of the dead trees, leaves, grass and similar stuff that had ever died since the Jurassic period because we didn't have the fungi to break that matter down!

Or on a smaller scale, imagine if Dr. Florey hadn't found P. notatum on an orange in the marketplace and hadn't hidden some in his coat during the development of the antibiotic Penicillin? And on a still smaller scale, we enjoy both blue cheese and Ustilago maydis (Huitlacoche or "corn smut") in various food preparations here in Mexico.

Nevertheless, as a book collector you probably will agree that we don't particularly need nor want mold on books nor on other important papers or documents, a point of view that quite a few experts have made amply clear. [1][2][3][4][5][6][7][8]9][10][11][12][14]

Thank you again for the discussion, we'd be glad to hear further from you in this matter, particularly I'd like to know more about foxing on books and papers.

See these articles about mildew

Reader Question: what's the best way to remove mold from a book?

I realize that you generally restore items for people, but I'm in a heck of a bind and am hoping that you can advise me. I have a book with green mold on the paper and need to remove the stain as much as possible. As it is to be for Christmas, I can't let it go the way it is. Is there any truth at all to ethyl alcohol or a diluted bleach solution being effective? I would be very careful not to wet the paper too much... Any information would be sincerely appreciated as I really am in a tough spot. Thanks in advance for any insight, - S.J. 12/15/12


SJ, in addition to the article above on book mold, check the expert citations in the references below, and also take a look at the cleaning suggestions also found for a different staining material found in foxing on books and papers - see FOXING STAINS on BOOKS & PAPERS

Reader Question: how can a homeowner clean moldy books?

Thank you for your excellent website concerning mold, it has been most useful.

We have some specific questions concerning mold on some of our books and will be happy to pay you for your time to advise us.

A little background first. We live in an un-airconditioned house (first construction started 1982) in Saugerties, NY. Interior relative humidity in the summer can run as high as 90-100%. In the winter with the wood burning stove operating full time the average season long humidity is 25%-30%. Several years ago my wife started to develop rather sever reactions (stuffed up ears, cough, runny nose, tightness in chest) which we attributed to mold in the house.

A year ago last summer we had a mold remediation contractor go over the entire house-we disposed of a lot of potentially moldy stuff, moved most of our books out of the house and the reactions seemed to lessen to a great degree. We now run a de-humidifier in the sealed crawl space keeping the summer humidity in this area below 55% RH since the remediation contractor felt that a lot of the problem was coming from the crawl space. This winter we started to bring some of our books back into use and my wife started to experience the symptoms again.

From your website it seems that hepa vacuuming of the exterior of the books is the first step- my questions are as follows: - J.K. & J.W. 11 Jan 2015

... [questions & our replies are below]

Reply: tips for DIY moldy book cleaning

Kudos for asking really good questions. I'll try a succinct reply and you can let me know what more you need to know.

Should we change the brush on the wand of the vacuum very frequently to avoid spreading the mold with the brush?

You're right about the chances of spreading mold. First be sure it's a HEPA vacuum or you'll make significant airborne mold levels.

I'd Vac the books outside if you can and when weather permits. Rather than changing the brush I'd physically remove as much mold and dust as you can, then use disposable clean wipes, folding as needed but do not move a moldy wipe on to the next book.

Can we kill any remaining mold by storing the books in an unheated area during the winter? If so, what temperature do we need to maintain and for how long?

Killing mold is not effective - you need to REMOVE the mold and correct the conditions under which it grew - "dead" spores may still contain mycotoxins, allergens, and possibly other trouble.


For books that have not been opened or used during the several year long contamination period should we expect the mold to be inside the pages or just on the surface of the exterior?

In the moldy library where I examined a great number of books, mold caused by recent area conditions tened to be on the book exteriors. Older books or books that were wet are more likely to have interior mold or foxing.

Examine each book to decide how much attention it needs and to decide if the cost and trouble of cleaning are justified. Moldy, superficially-cleaned books that are of some value but that you don't want to have professionally treated can, once cleaned as much as you can clean them, be stored dry in dry air-tight containers if necessary, pending other use or steps.

What should we use to wipe the books down with after the vacuuming? Is a cloth lightly dampened with water just as effective as any thing else?

Disposable sterile wipes are probably best. I saw significant cross-contamination when a mold remediator tried wiping many books with the same cloths even though they were rinsing them.

Can a non-scientist check for mold on books using a good light microscope and the photos from your website? If so what is the procedure? What concentration of mold or mold spores is acceptable for a household environment? (I am assuming that no-matter-what we will not be able to completely eliminate all microscopic evidence of mold)

If you see visible mold you'll recognize it - or see our photos of what mold looks like on surfaces.
If you physically remove dust and debris and visible mold you're doing what a lay person can reasonably do. A non-expert won't be able to make reliable microscopic examination of books or dust for mold though you might recognize some mold genera/species.

Are there other ways of checking for mold short of sending in tape strips to a pay-for-services company?


Other methods such as air tests and cultures are unreliable when negative tests are obtained. Those problems are discussed at MOLD TESTING METHOD VALIDITY

Should we definately start dehumidifying the living area of the house during the high humidity seasons? Can you recommend a specific brand and/or type of de-humidifier?


Other DIY mold cleanup references you may want to read include


Continue reading at FOXING STAINS on BOOKS & PAPERS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see MOISTURE CONTROL in buildings

Or see HOARDING HAZARDS for a discussion of book hoarding disorder hazards


Suggested citation for this web page

BOOK MOLD, CLEANING at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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