Leather is an extremely porous material, so you should always consider this restraint to be fluid-bonded with whatever partner you use it on naked. Sweat, lubricants, or any other bodily fluids will absorb into this riding crop, so it's best to limit the use of this BDSM device to one partner. For even better results, it's best to use mild unscented soap, since leather can soak up any unwanted scents that get on the surface. If your leather looks like it's getting moldy or getting an unwanted film on it, leave it out in the sun for a day and try to wipe it down the best you can with a cloth.
If you're using soap and water on this, it's best to sun-dry the riding crop, as it will dry it faster and prevent any unwanted mildew forming. If your riding crop looks dry or feels unusual in your hand, you could wipe it down with a leather conditioner. These can be found in shoe stores, leather shops, and online stores usually. Follow the directions on the leather conditioner bottle if you're using this, and your leather should start looking as good as new in no time at all. Do NOT submerge this leather riding crop set in water. The water will soak through and create places for harboring bacteria and mold.