What fungus generally causes itchy red skin?

All fungi: All fungi trichophyton, microspsporum etc can cause itchy red skin and should be treated with topilcal antifungals and if extensive oral antifungals such as lamisil, (terbinafine) Nizoral or sporonox.

May not be fungus: In my experience, most fungal infections do not itch. They cause burning sometimes, particularly in the groin and on the feet; but if you have an itchy red rash, it could easily be eczema, which does not respond to antifungal treatment. This is a common error. So if you apply an antifungal cream and nothing happens, see a dermatologist for a proper diagnosis.