Fungi are primitive microorganisms present everywhere in the environment, and commonly occur in nature in the form of yeast or mold. Human exposure is inevitable, but only about half of all types of fungi are harmful. Some fungi produce spores which can invade human tissue either through the skin or by inhalation. A weakened immune system makes you more susceptible to fungal infections, which range from a superficial, localized skin condition to a serious lung, blood, or systemic disease. Superficial infections include yeast infections, jock itch, athlete’s foot, barber’s itch, and scalp, hair, and nail infections. Most superficial fungal infections are easily treated with proper diagnosis and medications. But if left untreated, some superficial fungal infections can spread to the blood or lungs, significantly increasing health risks.