Mold is a common and normal fungal growth that occurs naturally. Without it, many life functions would not function properly. Unfortunately, when an over supply is present, allergic reactions can occur within the human respiratory system. Allergenic molds are common and abundant. Carcinogenic molds, on the other hand, can pose serious heath related affects that can cause serious harm to the human system.
Molds (or moulds; see spelling differences) include all species of microscopic fungi that grow in the form of multicellular filaments, called hyphae. In contrast, microscopic fungi that grow as single cells are called yeasts. A connected network of these tubular branching hyphae has multiple, genetically identical nuclei and is considered a single organism, referred to as a colony or in more technical terms a mycelium.
Molds do not form a specific taxonomic or phylogenetic grouping, but can be found in the divisions Zygomycota, Deuteromycota and Ascomycota. Although some molds cause disease or food spoilage, others are useful for their role in biodegradation or in the production of various foods, beverages, antibiotics and enzymes.
SOME COMMON MOLDS
Cladosporium is a genus of fungi including some of the most common indoor and outdoor molds. It produces olive-green to brown or black colonies, and its dark-pigmented conidia are formed in simple or branching chains.
The many species of Cladosporium are commonly found on living and dead plant material. Some species are plant pathogens; others parasite, other fungi. Cladosporium spores are wind-dispersed and they are often extremely abundant in outdoor air. Indoors Cladosporium species may grow on surfaces when moisture is present.
Cladosporium fulvum, cause of tomato leaf mould, has been an important genetic model, in that the genetics of host resistance are understood. 
 Health Effects
Cladosporium species are rarely pathogenic to humans, but have been reported to cause infections of the skin and toenails, as well as sinusitis and pulmonary infections. If left untreated, these infections could turn into respiratory infections like pneumonia.
The airborne spores of Cladosporium species are significant allergens, and in large amounts they can severely affect asthmatics and people with respiratory diseases. Prolonged exposure may weaken the immune system. Cladosporium species produce no major mycotoxins of concern, but do produce volatile organic compounds (VOCs) associated with odours.
Aspergillus is a genus of around 200 molds found throughout much of nature worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Micheli was reminded of the shape of an aspergillum (holy water sprinkler), and named the genus accordingly.
Species of Aspergillus are important medically and commercially. Some species can cause infection in humans and other animals. Some infections found in animals have been studied for years. Some species found in animals have been described as new and specific to the investigated disease and others have been known as names already in use for organisms such as saprophytes. More than 60 Aspergillus species are medically relevant pathogens. For humans there is a range of diseases such as infection to the external ear, skin lesions, and ulcers classed as mycetomas.
Other species are important in commercial microbial fermentations. For example, alcoholic beverages such as Japanese sake are often made from rice or other starchy ingredients (like manioc), rather than from grapes or malted barley. Typical microorganisms used to make alcohol, such as yeasts of the genus Saccharomyces, cannot ferment these starches, and so koji mold such as Aspergillus oryzae is used instead.
Members of the genus are also sources of natural products that can be used in the development of medications to treat human disease.
Perhaps the most well-known application of A. niger is as the major source of citric acid; this organism accounts for over 99% of global citric acid production, or more than 4.5 million tonnes per annum. A. niger is also commonly used for the production of native and foreign enzymes, including glucose oxidase and hen egg white lysozyme. In these instances, the culture is rarely grown on a solid substrate, although this is still common practice in Japan, but is more often grown as a submerged culture in a bioreactor. In this way, the most important parameters can be strictly controlled, and maximal productivity can be achieved. It also makes it far easier to separate the chemical or enzyme of importance from the medium, and is therefore far more cost-effective.
Stachybotrys is a genus of molds, or asexually-reproducing, filamentous fungi. Closely related to the genus Memnoniella, most Stachybotrys species inhabit materials rich in cellulose.
The most infamous species, S. chartarum (also known as S. atra) is known as "black mold" or "toxic black mold," and is frequently associated with poor indoor air quality that arises after fungal growth on water-damaged building materials. It is known to produce trichothecene mycotoxins including satratoxins.
Exposure to the mycotoxins present in Stachybotrys chartarum or Stachybotrys atra can have a wide range of effects. Depending on the length of exposure and volume of spores inhaled or ingested, symptoms can manifest as chronic fatigue or headaches, fever, irritation to the eyes, mucous membranes of the mouth, nose and throat, sneezing, rashes, and chronic coughing. In severe cases of exposure or cases exacerbated by allergic reaction, symptoms can be extreme including nausea, vomiting, diarrhea and bleeding in the lungs and nose. [