Depends on the tanning chemicals used. Some cheaper holsters may use chemicals that can help corrode the guns along with moisture the leather picks up from the atmosphere. Better holster makers generally use leather that has the proper tanning process that avoids that. The key is low humidity and all will be well. However, I keep my pistols in Boyt handgun rugs/cases when not in use. Cartridges can definately become corroded in belt cartridge holders if left in too long. No matter what leather used.