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What is Green Mold?

Soo Owens
Soo Owens

Green mold is an umbrella term that refers to a number of species of fungus with spores that take on a green tint. The more common species usually belong to three genuses of fungi: Cladosporium, Aspergillus and Penicillium. There are health hazards associated with the spread of green mold in areas frequented by people, and much like other mold variants, if the mold manages to penetrate households and hidden spaces, it can be difficult to remove it completely. Some mold species are relatively benign when exposed to people, while other species can cause more serious health problems that range from infections to extreme allergic reactions and toxic poisoning.

In broader terms molds are microscopic fungi that sustain themselves on many different surfaces all over the environment. Molds spread by producing tiny spores that can infiltrate almost any space, from where they reproduce and spread under the right conditions. These spores determine what color the particular mold species will assume. Not all fungi species that are classified under Cladosporium, Aspergillus or Penicillium will manifest as shades of green as species can differ from each other in color and scope of their effect.

Green mold species are a common cause of food spoilage.
Green mold species are a common cause of food spoilage.

Fungi species of the genus Cladosporium are very common molds that can be found in both enclosed areas and outdoors. Cladosporium species that appear as green mold are usually olive green in color. They thrive on plants in particular, and their spores are significantly present in the air. If Cladosporium manages to enter a household, it can usually be found on surfaces such as walls, insulation and wood framing but mostly in areas prone to constant moisture. Health concerns related to Cladosporium usually concerns its allergenic properties, as an abundant presence of spores could trigger symptoms in people with asthma or respiratory problems.

The mold that produces pencillin is a useful form of green mold.
The mold that produces pencillin is a useful form of green mold.

Species classified under the Aspergillus genus also produce common varieties of green mold. These green mold species prefer highly oxygenated environments and are a common cause of food spoilage. They prefer to grow on bread and other starchy foods, but they also have the ability to grow in areas that are depleted or completely deprived of nutrients, as is the case for the Aspergillus mold known as mildew.

Aspergillus will spread indoors, especially in moisture rich areas, and can pose a significant threat to a person's health, as some species of can be allergenic and pathogenic. Aspergillus flavus is one toxic mold species that possesses pathogenic properties. It can produce specific toxin called alflatoxin that is highly carcinogenic.

Penicillium species are well known for producing the antibiotic penicillin, a medically valuable compound that can eliminate some bacterial infections. The spores of Penicillium are some of the most common green mold species. They have a preference for cool, moderate environments, such as soil. Like Aspergillus, green mold species of the Penicillium genus can also contaminate food supplies. While some species produce the highly beneficial penicillin, other types can emit mycotoxins, toxins specific to fungi, the effects of which can cause significant harm on exposure.

Discussion Comments


I know that the mold in blue cheese is beneficial but I can never get myself to eat it. What type of fungus is in blue cheese? Is it penicillium?

Isn't it weird that something that we consider to be bad for the most part can be good in some cases?


@fify-- Believe it or not, mold doesn't have to be green. There are other types of mold like yellow mold, black mold, etc.

We tend to assume that all mold is green because the household mold we come across frequently has a greenish color.

If the only type of mold you've encountered is green, I think you should be happy. Some mold types, like black mold, can be very dangerous. Black mold is very toxic and can even cause death. Green mold varieties can cause allergic reactions too, but they're relatively harmless when compared to black mold.


Aren't all molds green? Why don't we just say "mold?"

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    • Green mold species are a common cause of food spoilage.
      Green mold species are a common cause of food spoilage.
    • The mold that produces pencillin is a useful form of green mold.
      By: catolla
      The mold that produces pencillin is a useful form of green mold.