Leather Properties and Care
How to Identify and Prevent Mold on Leather
Yes. Leather molds when humidity stays above about 65%, feeding on residues. Learn the signs, the look-alikes and four ways to keep stored leather dry.
Yes, leather can get moldy. Conservators class leather as particularly prone to mold, because leftovers from use and from care products feed it. Growth is encouraged when relative humidity (RH) sits between 65% and 100%, especially in warm, still air. Look for spots or a fuzzy film and a musty smell. Prevent it by keeping leather dry and ventilated with RH below 60%.
This answer is part of our hub on leather properties and care.
Why leather gets moldy
Mold feeds on what sits in and on the leather, including body residues from wear and the treatments applied to it. Fungi also feed on the animal fats in leather dressings when the air is humid, and dressings can trap moisture.
The Canadian Conservation Institute (CCI) gives these times before mold becomes visible on leather:
| Relative humidity | Time to visible mold | Facts |
|---|---|---|
| 90 to 100% | About 2 days | – |
| 80% | About 10 days | – |
| 70% | About 100 days | – |
| 60% | Growth just possible on some surfaces | – |
| Dips below 55% | Even short spells stop growth | – |
How to identify mold on leather
- Look. Mold grows low on the surface, either as isolated spots or across a large area. Brown to black growth shows up on light leather, and white or pale growth is common on dark leather.
- Smell. If several moldy items share a closed space, the smell may be the first sign. Stagnant air, as in a basement, makes the musty odor stronger.
- Mold or mildew? Mildew is the name for flat, thin, usually white mold growth. It is still mold.
- Rule out look-alikes. Fatty bloom from dressings, soap left by cleaners and salt from sweat can all look like mold. The checks are in leather spew vs mold and leather bloom vs mold.
How to prevent mold on leather
- Control humidity. The EPA says to keep indoor RH below 60%, ideally 30 to 50%. Conservators keep leather at a stable 45 to 55%, and below 30% it turns brittle.
- Dry it fast. Dry wet items within 24 to 48 hours. Leather should dry at room temperature, never in a dryer.
- Keep air moving. Poor air circulation encourages mold. Leather Collection's care instructions say to store leather somewhere cool, dry and well ventilated, away from damp cellars and hot attics.
- Go easy on dressings. Oils and fats in dressings can encourage biological growth. See what leather conditioner does.
If you already found mold
Mold slowly destroys the leather it grows on. Leather is porous, and a badly affected porous item may have to be thrown away; stains can stay after cleaning. Health risks and safe handling are covered in is mold on leather dangerous?. Removal steps are on hosob.com: how to remove mold from leather.
FAQ
Can I wipe mold off leather?
Wiping alone isn't enough. Dead mold can still cause allergic reactions, so it has to be removed fully, and the EPA suggests an N-95 respirator, gloves and goggles while you do it.
Does sunlight kill mold on leather?
We found no reliable source showing that it does. Conservators warn that direct sunlight discolors leather, dries it out and breaks it down chemically.
HitKB Editorial Team
HitKB articles are researched from published sources, cited in the text, and reviewed before publication.