The cracked skin that you may get at the back of the heels may be a painful condition if it is allowed to progress. This problem occurs when the skin around the backs of the heel is dryer and thicker than it should ordinarily be. When the callus builds up to make that dry thicker skin, it just cracks as it is not too supple or flexible. The crack that develops in the thicker skin, then tries to tear or rip the good skin under it. In the worst cases, this will become painful, can bleed and be an for an infection, so does need to be taken seriously. The reason for these cracked heels is not entirely clear. Some individuals simply have a tendency to have a dryer skin and some people, because of the way that they walk have a tendency to build up the callus around the periphery of the heel. Being overweight is also a risk factor for cracked heels. Shoes that are open at the back are also believed to play a part in this disorder.
The ideal way to take care of the cracked heels is to get a competent podiatrist to get rid of the thicker callused skin and then use an cream to make softer the rest of the skin. You could try and remove that skin yourself with something similar to a pumice stone or file, but that's a lot of work and needs to be carried out a lot. The emollient ointment used after this should be put on regularly to keep the skin well hydrated and supple. There quite a bit of opinion of what is the most effective lotion or emollient to use is and the best answer is the one which matches your skin. Some experimentation may be needed to get the best one. For cracked heels most podiatrists would recommend beginning with a urea based ointment.