The cracked skin that you may get around the edges the heels is often a painful condition 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 ordinarily be. As the callus increases to make that dry thicker skin, it just splits since it is not very supple or adaptable. The split that occurs in the thicker skin, then tries to split or rip the normal skin under it. In the worst cases, this will become painful, may bleed and become a portal for an infection, so does need to be taken seriously. The reason behind these cracked heels isn't completely clear. Some people just have a tendency to have a dryer skin and some people, because of the way that they walk tend to build up the callus around the periphery of the heel. Being overweight is also a risk factor for cracked heels. Footwear that are open at the back are also considered to play a part in this disorder.
The best way to manage the cracked heels is to get an experienced podiatrist to get rid of the thicker hard skin and then use an emollient to make softer the rest of the skin. You could try and get rid of that skin yourself with something such as a pumice stone or file, but that's a lot of work and needs to be carried out often. The emollient cream used after this has to be applied on regularly to help keep the skin well hydrated and flexible. There is a lot of opinion of what is the most effective cream or emollient to use is and the best answer is the one that matches your skin. Some trial and error may be required to find the best one. For cracked heels most podiatrists usually suggest starting with a urea based ointment.