Zygomycosis describes the infections caused by several related species of fungus that occur naturally in soil and decaying vegetable matter. The immune system of most persons can easily resist the fungus, but in individuals who are immunocompromised, it occasionally can grow within the human body. When it does affect a person, it grows faster than most other infections. It usually starts in the nose and sinuses and from there spreads to the digestive tract and skin.