What Causes Increasing Crust On Nipple?

I am 43, 156 cm 50kg with no significant medical history. i have a white crust on one nipple which has graudually been increasing but no other symptoms (no itchiness, redness, soreness or discharge) It looks similar to the crustiness I have on a mole which my doc saw ladt yaer and said was nothing to worry about. should i be concerned about the crust on my nipple?