Dryness or fungus
Feet often go through a cycle of wet/dry/wet/dry, from sweating, wearing shoes, taking shoes off, letting feet air dry, etc.
These changes can be hard on the skin and lead to cracking, flaking and thickening of the skin. Fungal infections, like athlete's foot
can cause the same findings, often with itching too. Other possible causes include eczema
, poor circulation, and others.