The cracked skin that you can get around the edges the heels is often a painful condition if it is allowed to develop. This condition happens when the skin around the backs of the heel is dryer and thicker than it should typically be. When the callus builds up to create that dry thicker skin, it just splits as it is not too supple or flexible. The crack that occurs in the thicker skin, then attempts to split or rip the good skin below it. In the most severe cases, this becomes painful, can bleed and be an for an infection, so does need to be taken seriously. The reason for these cracked heels is not completely understood. Some individuals simply tend to have a dryer skin and some people, because of the way which they walk have a tendency to build up the callus around the sides of the heel. Being overweight can also be a risk factor for cracked heels. Footwear that are open at the back are also considered to play a role in this problem.
The best way to manage the cracked heels is to get a skilled foot doctor to eliminate the thicker callused skin and then use an cream to make softer the remaining skin. You could try and get rid of that skin yourself with something like a pumice stone or file, but that's a lot of work and needs to be done often. The emollient ointment used after this has to be put on a regular basis to keep the skin well moisturized and flexible. There quite a bit of thoughts and opinions of what's the ideal cream or emollient to use is and the best answer is the one which suits your skin. Some trial and error may be required to get the best one. For cracked heels most foot doctors would suggest starting with a urea based lotion.