You're probably already all too familiar with mold and mildew that accumulates in the grout in your bathroom, or in your basement. Those same organisms can easily infect your horse tack and can ruin it if you don't take preventive measures.
In fact, mold is one of leather's worst enemies. An insidious organism, mold spawns hundreds of thousands of tiny offspring that can be carried from a small spot on a saddle to bridle and boots by cleaning rags or a puff of wind.
Mold and mildew, words that are often used interchangeably, come from the same family, but are actually slightly different in organic composition. Both are fungi - cousins to both salad mushrooms from the supermarket and the ones sprouting in your damp, warm manure pile. They are neither plant nor animal, but their own sub-category of living microorganism.
The difference between them is that mold tends to be green and hairy, while mildew is white-ish gray and powdery. Whatever their differences, you must vigilantly attack both to prevent them from spreading.
Because it thrives on moisture, mold grows best in 65% humidity or above. A mold problem begins with a single spore, but spores multiply rapidly and need no sunlight to grow. Mold can also grow in cold, damp environments, such as basements. The presence of mildew usually signals that the environment is ripe for mildew's bad cousin, mold.
Why is leather particularly susceptible to mold damage? Before it was made into a saddle, bridle or boots, leather was the skin of an animal. As such, it has three layers.
The top layer, or smooth side in most leather products, is the epidermis (or grain) of the leather. Just like human skin, the outer layer has pores, tiny holes into which dirt and mold spores can penetrate. The second layer is the corium (or "core"). The core is the protein fibers that form the leather's strength. Most good-quality saddlery is vegetable tanned to retain the core's organic structure. The third layer, called the "rough" and the side closest to the horse, is the outer fiber network layer (fibrils).
A single mold spot produces thousands of microscopic spores. If mold begins to grow on a piece of leather, it penetrates the pores in the grain and begins to eat away at the structural fibers (the corium), causing stains and weakening.
Mold living in a dark, damp basement or enclosed tack room, for example, will spread wildly because the recirculating air carries it to other items. Once you've got mold in a storage space, it is very hard to get rid of it. Besides causing nearly irreparable damage to your tack, mold can also cause allergies or even more severe health problems for humans.
Checking your tack for mold should be a part of every horse owner's routine, whether you live in Arizona or Florida. Even in dry climates, mold can grow in dark corners or after an unusually wet and rainy spell. Your first clue that you may have a mold problem will be the presence of a musty odor.