Darkening of the skin between my breasts from fungus?

Tinea versicolor: Tinea versicolor is a chronic yeast infection of the skin. The main symptom is patches of discolored skin with sharp borders and fine scale. This skin condition can be controlled but not cured. Treatment is with topical anti yeast medication like Nizoral cream or oral medication like ketoconazole.

Maybe not.: There are other causes of discoloration in that area; someone should do a KOH examination to be sure that's what it is. Other possibilities include a hormonal condition called acanthosis nigricans and collections of old, dead skin cells that wash off with alcohol, but not soap and water. (this is more common than generally realized.) see a dermatologist and get an accurate diagnosis/treatment.