The cracked skin that you can get around the edges the heels is often a painful condition if it is allowed to progress. This condition happens when the skin around the backs of the heel is dryer and thicker than it should normally be. When the callus increases to make that dry thicker skin, it just splits as it is not too supple or flexible. The crack that develops in the hard skin, then attempts to tear or rip the normal skin under it. In the worst cases of cracked heels, this will become painful, may bleed and become a portal for an infection, so does need to be taken seriously. The reason for these cracked heels is not totally clear. Some individuals simply tend 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 can also be a risk factor for this. Shoes that are open at the back are also considered to play a part in this condition.
The ideal way to manage the cracked heels is to get a competent podiatrist to remove the thicker hard skin and then use an emollient to soften the remaining skin. You could try and remove that skin yourself with something such as a pumice stone or file, but that is a lot of work and needs to be carried out a lot. The emollient ointment used after this ought to be put on a regular basis to help keep the skin well moisturized and supple. There is a lot of thoughts and opinions of what is the most effective lotion or emollient to use is and the best answer is the one that matches your skin. A bit of experimentation may be required to get the best one. For cracked heels most foot doctors usually suggest beginning with a urea based ointment.