What Is Foxing?

Foxing is the rusty brown or yellowish spotting that appears on the paper of older books — specks, blotches, or a diffuse mottling, usually on page edges, endpapers, and plates. It comes from age and storage: oxidation, traces of iron and other impurities in the paper, and humidity. It's cosmetic — it discolors the paper but doesn't normally affect readability — and while heavy foxing can lower a collectible book's value, the worst thing you can do is try to bleach it out yourself.

Published June 2026 · By Josh Eldred, New Mexico Literacy Project

What foxing looks like

If you open an older book and see a scatter of small reddish-brown spots, or a faint cloudy discoloration across the page, that's foxing. It tends to show up most on the outer page edges, the endpapers (the pages glued to the inside covers), and on illustration plates. The name is thought to come from the fox-red color, or possibly from "ferrous oxide" — the rust connection is apt either way.

What causes it

Foxing isn't fully settled science, but it's associated with a combination of factors: oxidation of the paper over time, metallic impurities (especially iron) left in the paper from manufacturing, and humidity, which can also feed microscopic mold activity. Cheaper, more acidic papers from certain eras are especially prone to it. That's why you see it so often in 19th- and 20th-century books and far less in either modern acid-free paper or very fine old rag paper. The common thread is moisture plus time — which is also the clue to slowing it down.

Does foxing lower value?

Sometimes — and it depends entirely on the book. Light foxing is expected in a genuinely old book; collectors of antiquarian material largely take it in stride, and it dents value only modestly. Heavy foxing — dense spotting across the text block, on a key plate, or on a dust jacket — is a more serious condition defect that pulls value down further, because at the collectible end buyers pay for clean paper. For an ordinary old book, foxing rarely changes much; for a fine copy of something desirable, unfoxed pages are part of what commands the premium. It factors into condition grading alongside everything else (see the condition grading guide).

Slowing it down

You can't reverse foxing without conservation, but you can keep it from spreading: store books somewhere cool, dry, and stable, out of damp basements and humid garages, with decent air circulation and away from direct sun. Stable moderate humidity is the single biggest lever. The full set of storage best practices is in the book preservation & storage guide.

Frequently asked questions

What is foxing in books?

Rusty brown/yellow age spotting on paper — specks or mottling on edges, endpapers, and plates — caused by oxidation, iron impurities, and humidity. Cosmetic, not a readability problem.

Does foxing lower a book's value?

Light foxing is expected in old books and matters little; heavy foxing on text, plates, or a jacket is a real defect that lowers value, especially on collectible copies.

Can you remove foxing?

Don't try at home — bleaching damages paper and shows. Professional conservation can sometimes reduce it but is only worth it for valuable books.