Molds grow best in warm, damp, and humid conditions. It spreads by making microscopic spores that are airborne. Mold spores can survive harsh environmental conditions, such as dry conditions, that do not support normal mold growth. Mold can grow in as little as 48 hours. Molds thrive in moist environments created by a flood, slow leak, broken pipe, or just high humidity. Molds need an organic food source. One common food source is cellulose, which is found in building materials such as wood and dry wall.