At least once a day a runner comes in with callous and blood blisters which have formed because of the callous burrowing into the skin. Time and again, I’m told that the person has been instructed not to remove the callous as it is protective in nature. Not true. Although callous initially builds to cushion and protect, eventually it becomes an irritant causing more harm than good.
The above images are of runners whose callouses have become blood blisters. If you have callous, either file it off or seek treatment with a Podiatrist to do it for you. Your feet will thank you.
Dr. Jenny Sanders Shoe Blog 
thank you so much for this post. at the start of each soccer season my teen gets such bad blisters underneath the calluses on the balls of her feet it becomes extremely painful for her to play or walk on them — now I know to take her to a podiatrist to get rid of them — we weren’t sure. plus, she says she won’t be able to play if the calluses are off and the blisters are exposed.