I pulled out shoes I haven’t worn all winter and found white fuzzy patches growing on the leather. What is this?

2. Why Mold Loves Your Winter-Weary Shoes
During winter, shoes are often stored away in closets or basements, where humidity levels can easily rise above 60%, the threshold where mold begins to thrive. Leather is a porous material, meaning it can absorb moisture from the air. When the ambient temperature fluctuates, condensation can form on the leather surface, providing the moisture mold needs to grow.
Additionally, organic residues like sweat, skin cells, and dirt left on shoes after the last use can serve as a nutrient-rich substrate for mold. Without regular cleaning and maintenance, these residues can exacerbate mold growth, especially during long periods of storage.
3. How to Tell If It’s Mold, Mildew, or Just Salt Stains
Distinguishing between mold, mildew, and salt stains is crucial for determining the right cleaning approach. Mold typically appears fuzzy and can be white, green, or black, while mildew might look more powdery and is often white or gray. Salt stains, on the other hand, appear as chalky white streaks or blotches and are more common in areas where road salt is used.
A simple test involves dampening a cloth with white vinegar and gently wiping the affected area. Mold and mildew will usually transfer onto the cloth, whereas salt stains will dissolve with the acidic solution, leaving a clear mark on the cloth. This identification step is key to choosing the correct cleaning strategy.