Heel cracks often occur when there is thickening of the skin of the heel which is not supple and flexible, so that minor pressure causes it to crack.
Gentle exfoliation after soaking the feet well will help some. The main way to manage this problem is to keep the skin very soft and flexible in that area. Use a moisturizer that has a keratolytic (a substance that dissolves thick keratin in the outer dead layer of skin called the stratum corium).
The moisturizer that works best for my patients is Am Lactin (available over the counter), which has ammonium lactate, a gentle keratolytic. The client must use it daily for several weeks to be effective. Do not apply it to the cracks because it can sting. The cracks can be sealed temporarily with liquid bandage (available in drugstores). Other keratolytics are urea and even some of the AHAs. If your client with cracked heels is diabetic, you must use extreme caution so that she does not get a serious infection in her skin. She should see her doctor if she has cracks anywhere on her feet that appear to be open sores.
Also, a type of fungal infection called moccasin tinea pedis can cause scaling and thickening of the heels. That would need to be treated with an antifungal cream. Lamisil cream and LotriminUltra (not regular Lotrimin) are the best over-the-counter antifungal creams; both were previously prescription antifungal creams (terbinefine and butenifine respectively) and are very effective. — Dr. Rich