According to the Center for Disease Control and Prevention, there are approximately 100,000 species of mold fungi, with fewer than 500 species described as disease-causing to humans. [5] The vast majority of household molds are not hazardous to humans, but many still have the potential to cause health problems. Molds produce allergens and irritants, and inhaling or touching mold or mold spores may cause allergic reaction to sensitive individuals. While reactions can vary between individuals, some of the most common symptoms include: