The cracked skin that you can get around the edges the heels may be a painful problem if it is allowed to progress. This condition occurs when the skin around the backs of the heel is dryer and thicker than it should normally be. When the callus builds up to create that dry thicker skin, it just splits since it is not very supple or flexible. The split that happens in the hard skin, then tries to tear or rip the good skin beneath it. In the worst cases, this will become painful, can bleed and be an for an infection, so does need to be given serious attention. The explanation for these cracked heels is not really completely understood. Many people simply have a tendency to have a dryer skin and some people, due to the way which they walk have a tendency to build up the callus around the edges of the heel. Being overweight can also be a risk factor for cracked heels. Footwear which are open at the back are also considered to play a part in this problem.
The easiest method to manage the cracked heels is to find a skilled foot doctor to get rid of the thicker hard skin and then use an emollient to make softer the remaining skin. You could try and remove that skin yourself with something like a pumice stone or file, but that's a lot of effort and needs to be carried out often. The emollient ointment used after this needs to be applied on consistently to help keep the skin well moisturized and flexible. There is a lot of opinion of what is the best lotion or emollient to use is and the best answer is the one which suits your skin. Some experimentation may be required to get the best one. For cracked heels most foot doctors would advise beginning with a urea based lotion.