Harmful Types of Mold Commonly Found in Homes

Harmful Types of Mold Commonly Found in Homes

October 11, 2020

Mold is found nearly everywhere, both indoors and outdoors, and most forms of mold pose little to no risks of health issues. That being said, there are some forms of mold that can prove harmful to the health of you and your family if allowed to flourish in your home. At DIYMoldTest.com, we believe that it is crucial to distinguish the harmful forms of mold from those that pose few health risks. 

Today, we will be looking at a few of the most harmful types of mold commonly found in homes. If one of these forms of mold is present in our home, there is a chance that you or a loved one may experience an infection or allergy associated with breathing in mold. While some of the health issues associated with exposure to mold are less rare than others, it is always best to educate yourself on the possible risks so that you are better prepared. With that, let’s get started!

Categories of Mold

Mold affects different people in different ways. While those with weakened immune systems may experience severe reactions when exposed to mold, others may not experience anything. This has led to much confusion as to how mold is potentially harmful. 

Greater confusion is also caused by the fact that the health effects caused by harmful mold types varies according to the type of mold. For this reason, different types of mold are broken up into a few different categories based on the health effects that they cause. Let’s take a look at those now:

  • Toxic mold: This form of mold produces harmful toxins, known as mycotoxins, that are poisonous to humans and can result in a variety of health problems.
  • Pathogenic mold: Pathogenic molds are capable of causing certain diseases and infections and are especially harmful to those with weakened immune systems.
  • Allergenic mold: Allergenic mold is mainly harmful to those with a predisposition to be allergic to mold. This type of mold also poses a risk to those with weakened immune systems.


When it comes to the more harmful types of mold commonly found in homes, Stachybotrys is one of the most potentially harmful. Known to many as “black mold”, Stachybotrys thrives in warm, moist indoor environments. Stachybotrys can cause a variety of different health issues ranging from flu-like symptoms and diarrhea to memory loss and severe respiratory damage. This form of mold is especially harmful for children as their lungs are still developing and their immune systems aren’t nearly as strong as adults.  

Stachybotrys can be identified due to its dark coloring but it should be noted that this form of toxic mold can also be dark green or gray in appearance. In terms of the odor it produces, Stachybotrys is commonly associated with a musty and/or mildewy smell. Stachybotrys most commonly grows within walls and ceilings. It can be difficult, in some cases, to test your home for Stachybotrys as it can be resistant to certain forms of air sampling. 


Another harmful form of mold that is commonly found in homes is Aspergillus. In total, there are 20 different species of Aspergillus. While not everyone is affected by the mycotoxins released by Aspergillus, each and every strain of this type of mold releases mycotoxins. Most often, Aspergillus grows on wooden surfaces and appears as small green or gray dots. Considering that Aspergillus thrives on wooden surfaces, it is common both indoors and outdoors. This type of common household mold has been shown to cause serious respiratory infections and allergies. 

In particular, Aspergillus is commonly associated with Aspergillosis, an infection caused by the inhalation of airborne Aspergillus mold spores. There are many different types of Aspergillosis and each type has symptoms that range in severity. While the less severe forms of Aspergillosis can cause symptoms similar to a sinus infection, more severe forms can result in cavities in the lungs that can have long-term health effects. Aspergillus has also been associated with health conditions such as severe asthmatic reactions and hay fever.


Similarly to Aspergillus, Penicillium thrives in both indoor and outdoor environments. There are also many different species of Penicillium and some are beneficial while others are potentially harmful. While some forms of Penicillium are used in the making of medicines and cheese, more harmful variations are known to cause health issues in those that possess weakened immune systems. 

Most commonly, Penicillium is known to cause allergies resulting in symptoms such as a runny nose, wheezing, and coughing. This form of common household mold is also known to cause bronchitis and asthmatic symptoms. Penicillium can be identified by the appearance of brush-like spores. 


Chaetomium is yet another potentially harmful variation of common household mold and is found most often in drywall that has been damaged by water build-up. Overall, however, Chaetomium favors dark, moist environments and can flourish anywhere from under carpets to behind wallpaper. Chaetomium is known for producing a musty odor and, due to its dark coloring, is often mistaken as Stachybotrys. 

In terms of potential health risks posed by Chaetomium, inhalation of its mold spores have been associated with neurological damage, autoimmune diseases, and allergic reactions. In terms of allergic reactions, common symptoms include runny nose and eyes as well as difficulty breathing.  


Fusarium is a bit more easily identifiable as types of mold go due to its pink, white, or reddish hue. Known mostly for growing on food products, Fusarium is able to adapt to and thrive, interestingly enough, in colder temperatures. This separates it from most forms of common household mold as it doesn’t necessarily have to be in a warm environment to grow. Fusarium has also been known to grow behind wallpaper and underneath carpet and other water-damaged surfaces. 

In terms of the harmful reactions caused by Fusarium in those with weakened immune systems, there are a variety of symptoms that can occur. This includes allergic reactions, such as sore throat, itchy eyes, runny nose, and dermatitis. In more severe cases, exposure to Fusarium can cause bone infections and even brain abscess. 

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