Mucormycetes, the group of fungi that cause mucormycosis, are present throughout the environment, particularly in soil and in association with decaying organic matter, such as leaves, compost piles, and animal dung. 1  They are more common in soil than in air, and in summer and fall than in winter or spring. 2-4 Most people come in contact with microscopic fungal spores every day, so it’s probably impossible to completely avoid coming in contact with mucormycetes. These fungi aren’t harmful to most people. However, for people who have weakened immune systems, breathing in mucormycete spores can cause an infection in the lungs or sinuses which can spread to other parts of the body.