From The Ordinary
Fungi and mold naturally occur in our environment. In fact, over 100,000 kinds fungi have been identified.
Fungi produce some very useful results. Yeast is a type of fungi used in preparing breads, bake goods and other food products, including some alcoholic beverages. The unique flavor of blue cheese is a result of mold. An edible mushroom is simply a type of fungi, and lifesaving penicillin is a product of mold (Penicillin chrysogenum).
Even though some forms of mold can add value to our lives, other forms can be harmful. Excessive amount of mold, different types of mold, and / or exposure to molds may present health effects for some people.
Mold is more likely to spread when an environment has been subject to moisture for a long period.