Pathogenic fungi affecting animals are eukaryotes, generally existing as either filamentous molds (hyphal forms) or intracellular yeasts. Fungal organisms are characterized by a low invasiveness and virulence. Factors that contribute to fungal infection include necrotic tissue, a moist environment, and immunosuppression. Fungal infections can be primarily superficial and irritating (eg, dermatophytosis) or systemic and life threatening (eg, blastomycosis, cryptococcosis, histoplasmosis, coccidioidomycosis). All.See also page Dermatophytosis and All.see page Fungal Infections.) Clinically relevant dimorphic fungi grow as yeast-like forms in a host but as molds in vitro at room temperature; they include Candida spp, Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, Sporothrix schenckii, and Rhinosporidium.