Diabetes, psoriasis, hypothyroidism, contact dermatitis, atopic dermatitis
and malnutrition should be ruled out first.
Itchy feet with tiny white blisters could be eczema, fungal infection, dermatitis, contact allergy with allergens like soap, chemicals etc. If you itch between toes too, there are chances that it is scabies, fungal infection and sweat dermatitis. See if your feet come in contact with particular grass, shrubs, chemical etc.