Depends on the cause. There are fungal infections which can cause this. I had it a few years ago. Moccasin Rosacea, iirc. The skin on one heel thickened, got a bit itchy, (I thought it was just hard skin) and then cracked. It was more a crevasse than a crack, about 1/4 ich deep, and very painful. I had to take antibiotic pills which took a few weeks to work.
Depends on the cause. There are fungal infections which can cause this. I had it a few years ago. Moccasin Rosacea, iirc. The skin on one heel thickened, got a bit itchy, (I thought it was just hard skin) and then cracked. It was more a crevasse than