How can i prevent bloody knuckles from my gloves/heavy bag?

in my work outs, i go about an hour to an hour and a half with my heavy bag, i was told my skin still needs to adapt to what i put it through. will my skin get calluses on my knuckles and webbings? i have mma gloves and they fit just right. so wrapping them seems out of the question (it'd be too tight), i heard vaseline will help but won't that ruin the inside of a leather glove? any suggestions how to prevent this or is this something i just have to go through until my skin adapts?