The three factors that cause bread to mold are the presence of spores, availability of a food source and optimal temperatures. Molds are microorganisms classified under kingdom Fungi.
Molds are microscopic plants, which contain spores that can germinate under favorable conditions. Molds produce a varicolored fluffy growth on a wide variety of foods, including bread. They can use different substances for their nutritional needs, even walls and window sills. Molds thrive when exposed to appropriate temperatures that range from 77-86 degrees Fahrenheit.
Molds are known to produce toxic substances called mycotoxins. Food products containing visible mold growth are not recommended for consumption.