The cracked skin that you may get around the edges the heels may be 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 normally be. As the callus builds up to make that dry thicker skin, it just splits since it is not very supple or flexible. The crack that happens in the thicker skin, then tries to split or rip the good skin below it. In the worst cases, this becomes painful, could bleed and become an for an infection, so does need to be taken seriously. The explanation for these cracked heels is not completely clear. Some individuals simply tend to have a dryer skin and some people, because of the way which they walk tend to build up the callus around the periphery of the heel. Being overweight can be another risk factor for cracked heels. Shoes that are open at the back are also believed to play a role in this disorder.
The ideal way to take care of the cracked heels is to get an experienced podiatrist to remove the thicker hard skin and then use an emollient to soften the remaining skin. You could try and get rid of that skin yourself with something such as a pumice stone or file, but that is a lot of work and needs to be done a lot. The emollient lotion used after this needs to be applied on a regular basis to keep the skin well hydrated and supple. There is a lot of opinion of what's the ideal lotion or emollient to use is and the best answer is the one which matches your skin. Some trial and error may be needed to get the best one. For cracked heels most podiatrists would advocate starting with a urea based ointment.