What is mould and where does it come from?

Mould is a type of fungus. It grows on surfaces in masses of branching threads which resemble dense cobwebs. The fertile threads, those which produce spores, often stand up from the surface into the air to release their spores. Spores are carried by air currents or by adhering to insects or animals. Active mould can be any colour, depending on the species and the substrate upon which it is growing. Mildew is another type of fungus, similar in structure to mould, but distinct as one species of fungus is distinct from another. The terms "mildew" and "mould" are not interchangeable; they are most often used in the common names of various fungi. Fungi is a kingdom of organisms, with a single division, Mycota. The fungi have traditionally been classified with plants but are now considered a distinct group of organisms.

Unlike plants, which produce their own food, fungi absorb nutrients from dead or living organic matter. Fungi also lack photosynthetic pigments. There are over 100,000 known living species of fungus, some of which are beneficial to mankind. Mycologists estimate that there may be as many as 200,000 more unidentified species of fungus. Yeast's, moulds, mildews, rusts, and mushrooms are types of fungus.

The spores of fungi that become mould or mildew are always present in the air and on objects. When the temperature and moisture in the environment are suitable for germination, the fungus spore bursts and grows into a threadlike filament called a hyphae. Using the object it is growing on as a food source, the hyphae form a mass, called a mycelium, and within a short time begin to produce spores. At maturity, spore sacs burst and release spores, which eventually land on other material and begin the reproductive cycle again.

Optimum conditions for mould and mildew development exist when temperature is above 70° Fahrenheit and relative humidity is above 70%. However, some common moulds can grow at temperatures as low as 50° Fahrenheit and in relative humidifies as low as 45%. It is also possible for moulds to begin growing in conditions of high relative humidity and temperature and then continue growing in environments with significantly lower relative humidity and temperature.