In some people the back of the heel can rub on shoes causing bony thickening. This tends to be towards the outside of the back of the heel and is termed a pump bump. This should not be confused with the changes that occur with a posterior heel spur / insertional Achilles tendonopathy.
A pump bump can make wearing most shoes extremely painful predisposing to hard skin formation or blistering and often the area looks very red.
Treatment options are limited and generally involve being careful with shoes (slip on shoes increase the rubbing) and wearing protective pads. The bump can be reduced by surgery. The traditional open approach can leave problems with scarring and take time to heal. Fortunately, minimal incision surgery is a realistic option and causes less scarring and a quicker return to activity.