Patient-related factors:
(1) poor prognostic factors (increased susceptibility, more severe disease)
(2) re-exposure
(3) nonadherence to antifungal therapy
Non-fungal nail disease (concurrent with or instead of fungal onychomycosis):
(1) bacterial infection
(2) trauma
(3) paraneoplastic nail disorder
(4) psoriasis
(5) other nail disorder
Drug-related:
(1) using a drug meant to treat a dermatophyte to treat Candida or a non-dermatophyte mold
(2) dermatophyte species resistant to the anti-dermatophyte drug
(3) inactive drug or loss of potency
(4) failure to reach fungus (inadequate dose, poor perfusion, poor penetration, presence of biiofilm)
(5) duration of therapy too short, with relapse
