Soak in vinegar or bleach for 10mins daily. (If it itches try the other)
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Don't try it if you have sensitive skin.
If both itches use baking soda mixed with water into a paste and brush it with a toothbrush (not the one you use for brushing your teeth)
Make sure you completely dry it cause bacteria loves moisture.
Stick a cotton swab near the area to dry it out.
Downside of this, is that your feet will become a lot drier usually especially with bleach.