Telltale green fuzz on the surface of bread is indicative that the bread is infected with mold, which can be dangerous to eat. Some conditions are more conducive to mold growth than others are.
Most molds grow best at warmer temperatures, according to the United States Department of Agriculture. Bread kept at room temperature instead of in the refrigerator is more likely to grow mold quickly.
Lack of Preservatives
Store-bought breads typically contain preservatives that help them resist mold growth. Homemade bread that does not contain preservatives is more likely to grow mold faster.
Exposure to Mold
Bread that is exposed to mold spores in the air or on people's hands develops mold sooner than bread that is not. Keeping the bread in an airtight container and washing hands before handling the loaf can help delay mold growth.
Mold thrives in a moist environment, so breads with high moisture content may grow mold sooner. If bread is freshly baked, it should be allowed to cool and dry out at room temperature before being placed in a container. Otherwise, the moisture and condensation in the container creates an environment conducive to mold growth.