Fungi reproduce by spreading microscopic spores.These spores are often present in the air and the soil but in general ,spores are everywhere ,and many strains grow on food. As long as the food provides perfect living conditions for the spore to survive,they spread.
Fungus needs four things in order to grow,
1.Water(moisture)
2.Food
3.Sustainable air quality
4.Temperature
The spores which are present abundantly, reside on moist surfaces thus producing fungal growth.