Does conditioner rot leather stitching? This is a common concern we receive here at Leather Milk. Stitch rot, while uncommon, can happen to leather, and when it does happen, it can be a problem. Rot can occur a few ways, be it mold, or over-conditioned leather, or the thread itself. Most leather items use synthetic threads that resist elements that promote rot, such as nylon and polyester, but very occasionally, you might find yourself in possession of a leather item with more organic stitching, such as cotton. Let's check out how these threads handle against adversity.
Cotton is an organic thread. The thread's quality is actually quite good on its own - cotton is fairly durable, and is very cheap. Next to nylon, it's among the most common materials used for threads. Unfortunately, cotton has some weaknesses. Cotton absorbs water and conditioner, takes longer to dry, has food value for bacteria, and can degrade outdoors. This fosters an ideal environment for rot potential, especially when the cotton stitching. This problem can be mitigated, somewhat, when the stitching is made from waxed cotton. This type of thread has natural resistance against water and oils, and will repel fluids well. Although this thread will likely last much longer than other cotton threads, it can still degrade under weather and sunlight. Cotton is particularly vulnerable outdoors, and as such, it is scarcely used to make leather products.
Nylon threads are synthetic, which gives them an edge. Nylon's known to be one of the tougher thread materials out there, with strong resistance to abrasion, aging, and stains, and resists water. Although its shiny aesthetic may not always be the best fit, you'd be hard pressed to find something that will hold leather together better than nylon. Its durability is so sound, in fact, that nylon is typically more stretchable than polyester thread. Quick drying time and easy clean make this thread an easy favorite. However, there are a few weaknesses this thread's got going against it too. First, it's not great environmentally. Nylon's made from oil refinery products - which are unavoidable byproducts - but still not cool. Second, while nylon is great outdoors, it's not the best. Prolonged UV exposure deteriorates nylon and can cause it to fade in color, and while this material resists water, it can still absorb it if the water is left to its own devices for very long.
Saddleback Leather Company uses these threads! Polyester's a great material, durable and abrasion resistant, resists stretching, shrinking, and fraying, and repels water much more strongly than nylon. This material is in a class of its own, maintaining with age, and built to endure weather and the great outdoors. It's a particularly good fit for leather, especially because it is so easily cleaned, and easily dries. As if this weren't enough, polyester is also powerfully UV resistant, and will hold its color and avoid fading. The thread's more environmentally friendly than nylon as well; while polyester is not biodegradable, it is more easily recyclable. The only two downsides to this thread is that polyester can stain a little more easily than nylon, and this thread does not breathe - meaning anything moving past the surface of this stitching can be difficult to remove.
Fundamentals of Rot
Now that we've got an idea about the different types of threads you'll be encountering, let's examine how they can be vulnerable to rot. The first thing to know is that rot needs moisture and warmth to happen. If conditioner sounds like a great way to make this happen to you - you'd be right. That's not the end of the story, though. Leather breathes, and good stitching allows conditioner to keep up this absorption, rather than remain dormant. As old oils are used up, they are replaced, and the cycle goes on, keeping a fresh hide. When moisture or conditioner gets stuck in one place for too long, however - such as when leather is over-conditioned - this creates an environment where bad things can happen: be it mold, mildew, or rot.
Here's the good news. The majority of threads used on leather will not rot. Synthetic threads, like nylon and polyester, which make up the bulk of threads used to make leather items, contain no food value for bacteria, and so won't be susceptible to rot their own. Rest easy.
That doesn't mean your leather itself won't have any problems. You can read about taking care of mold and mildew here. Suffice it to say, a little care goes a long way. But on the off occasion you've got cotton threads, or they've gotten pretty messed up, the best thing to do is clean them. Alcohol's the best way to go here, deeply cleansing materials and pulling out bacteria with unparalleled ease. You can also go with a holistic approach, regulating the material's environment by giving it lots of ventilation and exposure to dry, cool environments.
Actual, honest to goodness rot, however, is a bad thing to have, and nearly impossible to treat. Often times, it's best to simply replace the leather stitching. If the affected area is small, however, you can also burn the ends of the stitching in place, a little past the quarantine zone on your stitch.
Stitching Back Together
So here's what you should carry away from all this. Most leather stitching is designed to take care of itself. If it's synthetic, conditioner should pose no threat to it. This doesn't mean you should neglect the leather itself - very often, the healthy of your thread will correlate directly with the health of your leather. If your thread is organic, it may be more important to keep it clean, and take care when conditioning. If you are in doubt about the material, try to look it up online, or ask the tender selling the leather to you. When treating it, always check for any leather care instructions included from the manufacturer, and test the recipe first.
Hope this helps!