Medical Dermatology - Infections
Humans are natural hosts for many bacterial species that colonize the skin as normal flora. Staphylococcus aureus and Streptococcus pyogenes are infrequent resident flora, but they account for a wide variety of bacterial pyodermas. Predisposing factors to infection include minor trauma, preexisting skin disease, poor hygiene, and, rarely, impaired host immunity.
Fungal and yeast infections
Three fungal genera—Trichophyton, Microsporum, and Epidermophyton—account for the vast majority of infections. Fungal reservoirs for these organisms include soil, animals, and infected humans.
Herpes simplex virus (HSV) infection is a painful, self-limited, often recurrent dermatitis, characterized by small grouped vesicles on an erythematous base. Eighty-five percent of the population has antibody evidence of HSV type 1 infection. HSV type 2 infection is responsible for 20% to 50% of genital ulcerations.