Book care guide
Store old books upright on shelves in a cool, dry, steady room, out of direct light. The Library of Congress says 70 °F (21 °C) or below and 30 to 55% relative humidity is safe for most books, and that humidity above 60% risks warping and mould. Check your room below, then tick any signs you see on a book to get the likely cause, what is safe to do yourself and when to call a conservator.
Ex libris · Dragon Bookcase Example
This result belongs to a room at 18.0 °C (64.4 °F) and 62% RH
Storage check
Too damp
Steady matters as much as the number: NEDCC warns that rapid swings distort paper and bindings.
Ex libris · Dragon Bookcase Example
This result belongs to a book with musty or mildewy smell
Condition check · 1 sign
Musty or mildewy smell
An earthy smell with no visible growth. NEDCC notes a musty smell can come with active mould, and may or may not linger with dormant mould.
Conservator: If the smell comes back, look again for mould, and for damp in the room or bookcase.
General information, not medical or conservation advice. For a valuable or fragile book, ask a conservator: the American Institute for Conservation and, in the UK, Icon list professionals. If mould is making you unwell, or you have asthma, allergies or a weakened immune system, talk to a doctor before touching it.
Paper, glue and leather all respond to heat and moisture. NEDCC explains that higher temperatures speed up the chemical reactions that make materials deteriorate, and that damp brings mould and pests. The figures differ a little between sources, so the checker uses the Library of Congress range as “good” and NEDCC’s wider one as the outer limit.
| Source | Temperature | Relative humidity |
|---|---|---|
| Library of Congress, home books | 70 °F (21 °C) or below | 30–55% |
| NEDCC, rooms shared by people and collections | 64–72 °F (about 18–22 °C), not over 75 °F (24 °C) | 30–60% |
| UK National Archives leaflet (2005) | 13–19 °C (about 55–66 °F) | 45–60% |
Steadiness matters as much as the number. The Library of Congress warns against frequent swings, and NEDCC says rapid changes distort paper and bindings. Too dry is a problem too: the Library of Congress says humidity below about 30% can warp books as they contract. That is a winter risk: the Canadian Conservation Institute notes that cold weather outside and dry central heating can push indoor humidity under 30%, so between December 2026 and February 2027 check the reading again with the heating on.
NEDCC suggests keeping books at least three inches (about 75 mm) away from exterior walls, which follow the temperature outside, and never storing them directly on the floor. The Library of Congress advises against basements, attics and garages, and against vents and radiators; the Canadian Conservation Institute adds plumbing pipes and the top of a shelving unit. Keep books out of direct light: NEDCC says visible light fades colours, ultraviolet speeds up the embrittlement of paper, and the damage is cumulative and irreversible. Blinds, curtains or UV film on south- and west-facing windows help.
Active mould looks fuzzy or slimy and may smear when touched, according to the Library of Congress and NEDCC; dormant mould is dry and powdery. The CDC says people with asthma or a mould allergy may have severe reactions, and NEDCC says people with weakened immune systems should not handle mould at all. For anyone else, the Library of Congress advises nitrile gloves and an N95 mask. Move the book away from the others to a dry room, dry it, and only then remove dry mould with a HEPA-filter vacuum or outdoors. Freezing a wet or actively mouldy book for at least 24 hours holds back further growth until it can be dried or cleaned, NEDCC says. Don’t seal a damp mouldy book in a plastic bag unless it is going straight into the freezer, and don’t reach for bleach. If mould covers more than about 10 square feet (roughly 1 m²), the EPA says to follow its guidance for larger clean-ups.
A smell with no visible growth is still a sign of damp, past or present. The Library of Congress suggests standing a hardback slightly open so its pages fan out, for several days, then keeping it somewhere cool with air moving at 35 to 55% humidity, where musty odours fade over time. For a stubborn smell, it suggests a closed container with activated charcoal or baking soda for several days, with the book kept from touching it, checking often for mould.
Clean, dry hands are better than cotton gloves: the Library of Congress and the British Library both say gloves make pages harder to turn safely. Take a book off the shelf by the middle of its spine, pushing its neighbours in first, never by the top of the spine. Skip the sticky tape, even tape sold as “archival”, and leather dressings; for a loose binding, the Canadian Conservation Institute suggests tying the book with flat cotton tape until a conservator can look at it.
All checked on 5 November 2026.
Upright on shelves with bookends, large books flat, in a room at 70 °F (21 °C) or below and 30 to 55% relative humidity, as the Library of Congress advises. Keep them out of direct light, off the floor, away from outside walls and radiators, and out of attics, basements and garages.
Isolate the book in a dry room, let it dry, then remove the dry mould with a HEPA-filter vacuum or outdoors, wearing nitrile gloves and an N95 mask. Freeze a wet or actively mouldy book for at least 24 hours if you can’t dry it at once. Don’t use bleach, and ask a conservator for anything valuable.
Check for mould first. Then air the book standing slightly open for several days, and keep it cool and dry at 35 to 55% humidity. For a stubborn smell, the Library of Congress suggests a closed box with activated charcoal or baking soda, not touching the book, for several days.
The Library of Congress says 30 to 55% relative humidity, kept steady. Above 60% risks warping and mould; below about 30% can warp books as they dry out. NEDCC accepts up to 60% where people and books share a room.
Not for everyone. The CDC says people with asthma or a mould allergy may have severe reactions, and NEDCC says immunocompromised people should not handle mould. Others should wear nitrile gloves and an N95 mask and work in a ventilated space or outdoors.