A useful analogy is to think what happens when a tomato is squashed. As it is squashed, the tomato skin splits. This is what wants to happen to the skin around heel when we walk.
The main predisposing factors for this is being overweight as this will mean that there is more fat under the heel to expand out sideways and there will be more weight trying to compress the fad pad. Wearing no shoes or shoes that are open also predispose to this. A shoe helps keep the fat pad under the heel and prevent the expansion. If the skin is dry, it is also more likely to crack. Those with a callus or thickened skin also makes them more prone to cracked heels.

Once the skin cracks, the continued walking on it is not only painful, but keeps opening the crack making them hard to heal because of this. The force on the crack can be very high if the crack is in the thickened callused skin.

Treatment always has to start with the removal of the calluses or thickened skin by a Podiatrist. Next some tape or strapping is applied at right angles to the split to hold the edges of the crack together to allow healing to happen. The edges of the cracked skin can sometimes be held together with surgical glue.

So the skin can take the pressure, emollients and creams then need to be used to make the skin more flexible and supple~After the initial healing, then the dry skin needs to be treated to make the skin supple and flexible so that it will tend not to crack~{So the skin can take the pressure, emollients and creams then need to be used to make the skin flexible and supple}~Emollients and creams then need to be used to make the skin flexible and supple, so the skin can take the pressure}. Shoes that are not open in the heel area are important to prevent the expansion of the fat pad. A heel cup to hold the fat pad in place is sometime used. Regular foot care is then needed to reduce the thickened skin and keep the skin supple and moist.

For the latest research on this, see about heel fissures at Podiatry Arena, or ask a question about cracked heels at the Foot Health Forum.