Leather: Use a glycerin-based leather cleaner to remove dirt and grime, while keeping your leather hydrated and soft.
Nylon: Fill a bucket with water and mild dish soap, then use a scrub brush to remove any dirt or sweat build-up. Rinse reins and hang to dry.
Rawhide: Wipe down after every ride with a dry cloth. For a deeper clean, apply a rawhide cream. Hang to dry in the shade to avoid sun-bleaching.
Have Mold? Pour hydrogen peroxide on an old rag and wipe down any moldy spots you see. Then clean reins as normal.