What causes callus and cracks? Genetic skin type, hydration, skin thickness, muscle wasting, friction, bony prominences and disease processes like diabetes, psoriasis and thyroid dysfunction can all play a role. The Australian climate is particularly damaging to the exposed skin on the feet and heels, especially in summer. We put sunscreen and moisturiser on our face, hands and other exposed skin areas but we forget about our feet. As Podiatrists, we know what a difference a regular foot moisturising routine can make.