Mucor mould, also known as black fungus, computer illustration. Mucor sp. fungi are found in soil and decaying organic matter and are common indoor moulds. It can cause the rare but serious disease mucormycosis (zygomycosis) in patients that are immunocompromised or undergoing steroid therapy. The fungus can infect the lungs, sinuses, brain, gastrointestinal system, or the skin. In 2021 outbreaks of mucormycosis were seen in diabetic patients with Covid-19. Treatment is with antifungal drugs, although surgery is often needed to cut away the infected tissue.