Causes
Opportunistic infections (infections that are caused by a diminished immune system) are frequent. Fungus from other parts of the body (commonly tinea pedis or 'athlete's foot') can contribute to this itch. A warm, damp environment allowing the fungus to cultivate greatly contributes; especially with tight, sweaty or rubbing clothing such as a jockstrap.
The type of fungus that most commonly causes tinea cruris is called Trichophyton rubrum. Some other contributing fungi are Candida albicans, Trichophyton mentagrophytes and Epidermophyton floccosum.
Read more about this topic: Tinea Cruris