Glove oil is very frequently seen being used by professionals. It is a light, all-purpose oil that has been specifically designed in order to be able to penetrate the material of most baseball mitts for two reasons: that of helping to break in new mitts by softening the material, and of keeping old mitts fresh and pristine by infusing them with much-needed oils so that it doesn't become dry and crackly. It can be used without worry, as even if you put too much oil on your mitts, then you're not going to damage them. Furthermore, glove oil dries quite quickly and doesn't leave residue, either, making the whole process quite easy. Keeping your mitt well-oiled can help protect against things like mold and mildew.