Bread mold grows fastest in areas that are dark, warm and damp. It is possible for mold to grow in cooler, drier or more brightly lit conditions, but the mold growth is slower in such environments.
The U.S. Department of Agriculture recommends keeping food covered, maintaining household humidity at or below 40 percent and examining foods carefully for mold prior to purchase. Following these recommendations minimizes the chance of mold growth on bread or other foods. According to USDA guidelines, baked goods, such as bread, must be discarded if contaminated with mold. Due to the porous nature of these foods, mold contamination spreads below the surface and renders the entire food item inedible.
While not all forms of mold are dangerous, and some are even used to produce aged cheeses, bread mold is not edible. Harmful molds contain cancer-causing toxins called aflatoxins,and even non-toxic molds may cause allergic reactions in sensitive individuals. Even inhaling mold spores while smelling food for signs of spoilage can cause respiratory distress in people with sensitivities. Mold is also a common sign of bacterial contamination in food, since the same conditions that foster mold growth encourage bacterial growth. Molded food should always be treated as spoiled.