Distal Subungual Onychomycosis Toenail Fungus Disease The most common kind of infection that is caused in the nails is named DSO (Distal Subungual Onychomycosis). Athlete's foot is caused by this nail fungus. The skin underneath the toe nail is infected by this fungus, and it begins infecting the toe nail. Learn more on indications and healing for different forms of nail fungus with all the treatments available including natural remedies, topical treatment options and prescription drugs.