How do you get rid of really bad athletes foot rashes? does sunlight (lots of it) kill the fungus?

Couple of things: Exposure to sunlight does help. But you probably need to use and antifungal medication to help, as well as good hygiene.

Sunlight has no: Effect. When infected, you must treat it with at least a topical antifungal. Occasionally, an oral antifungal will be used if teh problem is severe enough. See your podiatrist or dermatologist, .