The more you wear your watch, the more its leather straps will become exposed to various elements, especially your sweat, causing it to have an unpleasant odour. This odour is caused by a build up of bacteria, and like our skin, leather needs to breathe and be cleaned. Fortunately, it is not too difficult to get rid of a smell on your leather wrist watch band.
Squirt a very small dab of non-corrosive soap--about half the size of a dime--on your finger, and gently rub it across the bottom and top of the first strap, making sure all areas are covered. Repeat this with the second strap.
Dampen a corner of your rag with lukewarm water. Rub the leather straps with the damp part of the rag to remove any excess soap.
Rub a dry part of the rag over the top and bottom of both leather watch straps until they are barely wet.
Place your watch in a warm, non-humid environment to dry for a few hours.
Repeat these steps every other day, or whenever your watch begins developing a strong odour, depending on how frequently you wear the watch.