Journal · From the Bench
Mould on leather, removed safely
Published 9 October 2026 · Gordon Mielke
How to tell mould from wax bloom, clean it safely and keep it away in a wet climate, using the Canadian Conservation Institute's method.
Every winter someone opens a closet in a basement suite and finds a fuzzy white bloom on a leather bag, belt or wallet. In a city as damp as Vancouver, mould on leather is a real risk, not a rare one. The good news is that it's preventable, and small outbreaks can usually be dealt with at home. This entry walks through how to tell mould from harmless wax bloom, how to clean it safely, and how to stop it coming back. The method comes from the Canadian Conservation Institute (CCI), the federal agency that tells museums how to care for leather artifacts.
Why leather grows mould
CCI's note on removing mould from leather explains that leather and skin objects are particularly susceptible because they hold onto materials from use and from care products applied to keep them supple, and those materials are food for mould. Mould spores are always in the air; they only grow when conditions suit them.
The conditions are specific. CCI says relative humidity between 65 and 100%, warm temperatures and poor air circulation promote mould growth, and that mould will generally grow after:
| Relative humidity | Time before mould generally grows (CCI) |
|---|---|
| 90–100% | about 2 days |
| 80% | about 10 days |
| 70% | about 100 days |
That table explains the classic Vancouver scenario. A wet bag goes into a closed closet, or a leather jacket hangs in a basement storage room with no airflow, and a few weeks later it's blooming. Wet leather in a sealed space is the worst case.
Is it mould or just wax bloom?
Not every white film is mould. CCI points out that oils, waxes and other products can form a white deposit on leather that's easy to mistake for it. Its separate note on caring for tanned leather adds that fatty blooms from dressings and soap residue tend to feel slightly waxy, while salts from perspiration are crystalline.
How CCI says to test it
Wearing gloves and a mask, dip a cotton swab in mineral spirits, blot it on paper towel, then roll it over a small, hidden spot. Wait about 15 minutes for the solvent to evaporate and look again. If the white deposit has gone, it was most likely a change in applied waxes rather than mould. CCI's rule if you're unsure: treat it as mould.
Mould usually looks different anyway. CCI describes it as a thin grey, green or white powdery deposit, or small black dots, and notes that the first sign may simply be the smell.
How to remove mould on leather safely
Mould is a health concern, so protect yourself first. For a small amount of visible mould (CCI's threshold is 1 m² or less, which covers any wallet, belt or bag), CCI recommends at minimum an N95 or N100 disposable respirator, disposable gloves, a disposable apron and non-vented goggles. People with allergies, respiratory conditions or a suppressed immune system shouldn't handle mouldy items at all.
- Isolate it. Seal the item in a plastic bag so spores don't spread to the rest of your closet. Label it.
- Dry it, slowly. If the leather is damp, it has to dry before cleaning. CCI recommends air-drying outdoors on a clear, dry day, away from people and air intakes, turning the item so all surfaces dry. If it smears when you brush it, it isn't dry enough yet.
- Or freeze it. If you can't deal with it right away, CCI says freezing (sealed in polyethylene, in a household chest freezer) is a quick way to stop active growth, though spores survive. Thaw it in the sealed bag, then open it and start drying straight away once it reaches room temperature, or the mould will grow again.
- Vacuum, don't wipe. CCI calls close vacuuming one of the most effective ways to remove mould. Hold the nozzle very close, let the suction lift the growth, and use a soft brush to guide stubborn spots toward the nozzle. Go over the whole item, not just the visible patch, ideally twice in perpendicular directions. A HEPA-filtered vacuum is strongly recommended so you don't spread spores.
- Clean up. Wash tools and work surfaces with water and detergent, then disinfect them (not the leather) with household bleach diluted ten times, with 10 minutes' contact time, as CCI describes. Bag and discard contaminated wipes and vacuum bags outdoors.
What not to do
- Don't dry it on a heater or in direct sun. CCI warns that local heat sources dry out and damage leather, and that sunlight causes discolouration and photo-chemical damage.
- Don't scrub damp mould into the surface. CCI advises limiting handling so mould isn't pushed into the leather.
- Don't re-seal it while damp. A sealed bag is for isolation or freezing, never for drying.
Even after careful cleaning, CCI notes that some spores and fragments are likely to remain. If a piece is heavily infested, or it's precious, talk to a professional conservator.
How to keep mould off leather in a wet climate
Prevention is mostly about humidity and air. CCI says that because mould needs relative humidity above 65% to grow, adequate humidity control and air circulation will prevent outbreaks, and recommends keeping leather at a stable 45 to 55% RH. Health Canada's home advice on preventing mould is to keep indoor relative humidity between 30 and 50%, and it suggests an inexpensive hygrometer from a hardware store to measure it.
- Dry wet leather before you put it away. Let a rain-soaked bag or wallet dry at room temperature with air around it. Our rain care guide covers the drying routine in detail.
- Skip the damp basement. CCI specifically says leather shouldn't be stored in damp basements, near sweating pipes or over radiators.
- Let it breathe. Store leather in cotton dust bags or wrapped in acid-free tissue, not sealed plastic. CCI notes that hygroscopic wrapping like cotton or acid-free tissue helps buffer humidity swings.
- Use it. Leather you carry every day rarely moulds. It's the bag at the back of the closet that blooms.
- Check stored pieces. CCI suggests museums inspect leather collections every three months for mould or insects. A quick seasonal look at your closet works the same way.
Built to be used, not stored
Every Rogue Artisan piece is cut from full-grain vegetable-tanned leather or Horween Chromexcel in my East Vancouver studio, and designed to be carried daily, which is the best mould prevention there is. That goes for a wallet and for a custom leather bag alike. If you're curious how the two leathers differ in the wet, start with Horween Chromexcel explained and what is patina. Have a question about a piece of mine that's been through a damp winter? Call (250) 719-1332 or email rogueartisan@outlook.com.
Frequently asked questions
What causes mould on leather?
The Canadian Conservation Institute says relative humidity between 65 and 100%, warm temperatures and poor air circulation promote mould growth, feeding on materials left in the leather from use and care products.
How quickly can mould grow on leather?
CCI says mould will generally grow after about two days at 90 to 100% relative humidity, 10 days at 80% and 100 days at 70%.
How do I tell mould from white wax bloom on leather?
Test a hidden spot with a cotton swab dipped in mineral spirits and blotted. If the white deposit is gone after about 15 minutes, it was most likely wax rather than mould. If in doubt, treat it as mould.
What is the safest way to remove mould from leather?
Wear an N95 respirator, gloves and goggles, make sure the leather is dry, then vacuum it closely all over, ideally with a HEPA-filtered vacuum, using a soft brush to guide stubborn spots toward the nozzle.
What humidity should leather be stored at?
CCI recommends a stable 45 to 55% relative humidity for leather. Health Canada advises keeping indoor humidity between 30 and 50% to prevent mould in the home.