I have a dark itchy rash on the top of my foot. what should ido?

Go see your doctor: Infection? Allergic reaction? Bug bit? Can't diagnose, much less recommend therapeutic options based upon your description. Go see your family doc or dermatologist who can examine you, make diagnosis & offer you appropriate treatment (if indicated).

Concerning: Anytime you have dark skin discoloration, it could be very soon. Please get it checked out by your podiatrist.

Rash: Ringworm, tinea, yeast, fungus....All dark, all itchy.....You should see your pcp, dermatologist, or podiatrist asap...

1 foot or both?: If 1 foot it is chronic nummular dermatitis which will improve with a prescription steroid cream. It is not contagious and the cream is safe. First the itch will stop, then the color will slowly (months) fade.