How does skin ‘crack’?

When skin is soft and supple, it bends when pressure is applied, just like a normally ripened tomato. On the other hand, if the skin dries out openings can occur between surface skin cells and these can ‘crack’ open, like an overripe tomato with force applied to it. This is why big people with dry skin on the heels and feet tend to get ‘cracked’ skin on the heels when wearing thongs or shoes over which the heel protrudes.