Molds are found almost everywhere. If you have an attic, basement, or crawlspace, or you have a moisture problem in your home, then there is a big chance that you have molds growing in your walls somewhere. While not all molds are dangerous, most people have a hard time telling what kind of mold is dangerous and what type it isn’t.

What Kind Of Mold Is Dangerous? How To Know Convincingly

Molds are microscopic fungi that look like fuzzy or hairy spots on walls, furniture, paper, carpet, and other upholstery items in the home. They come in a variety of colors including, gray, green, or black. They are more than 100,000 mold species, and asides from the destruction they cause to properties, most of these mold species are not harmful.

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Dangerous Mold Types In House, Basement, Bathroom, Etc.

Certain mold types may pose a severe health risk to people and pets in the home. There is a chance that you have heard of these so-called “toxic mold” at some point. But the truth is that molds themselves are not poisonous or toxic.

The toxic mold species are only considered dangerous because they are toxigenic. This means they produce toxic substances known as mycotoxins. Mold species that are allergenic and pathogenic are also considered deadly to human health. They do not only produce toxins but produce other substances that can adversely affect health.

1. Allergenic molds

Molds produce spores through which they reproduce and spread. But the spores produced by mold are airborne and can be inhaled. They can cause allergic reactions such as sneezing, runny nose nasal, congestion, and itchy throat. These allergenic mold spores can trigger asthmatic episodes and allergic reactions. The most common mold types that produce spores that trigger allergies include:

  • Alternaria: this is a genus of mold with more than 50 mold species. They commonly appear as dark gray spots that can grow both indoors and outdoors. They are typically found on bricks, wallpaper, plaster, and canvas. Common species in this group include A. tenuissima and A. alternate.
  • Aspergillus: this is among the most popular mold type in the world. Aspergillus molds are so common that is almost impossible to avoid them. However, they may pose a serious problem for immunocompromised individuals or those suffering from asthma and other respiratory problems. Aspergillus molds also cause allergic reactions in certain people.

Other common groups of molds that produce allergenic spores are; Penicillium, Cladosporium, Fusarium, etc. 

2. Pathogenic molds

This refers to a group of molds that can cause infections in humans. Pathogenic molds are generally more problematic than allergenic molds. While allergenic molds only affect immune-compromised individuals and those with allergic problems, pathogenic molds can affect anyone. Some species of molds, such as the Aspergillus genus are grouped, as both allergenic and pathogenic. Other types of pathogenic molds include:

  • Cryptococcus neoformans: this is a pathogenic mold that causes a type of fungal meningitis known as cryptococcal meningitis. Although most people can easily fight off infections caused by the spores of this mold, the inhaled spores can stay in the body of a healthy individual and trigger an infection later when the person’s immune system is weaker.
  • Histoplasma capsulatum: the infectious disease histoplasmosis is caused by spores of the H. capsulatum mold. It can also cause pneumonia. Infections caused by the spore of these fungi can be life-threatening. H. capsulatum mold is not very common in indoor spaces. They occur in the soil and may be released into the air during large-scale construction projects.

3. Toxigenic molds

Most times when people talk about toxic molds, they are most likely referring to toxic genic molds. However, we have established that pathogenic and allergenic molds can be dangerous as well. Toxigenic molds produce mycotoxins as byproducts of their metabolism. This chemical toxin is different from the spores produced by molds. But they can be airborne as well-traveling through the air with tiny dust particles in the air.

Common toxigenic molds that can be found in an indoor space include:

  • Fusarium species such as F. solani and F. oxysporum
  • Penicillium species such as P. citrinum, P. brevicompactum, and P. chrysogenum
  • Aspergillus species   such as A. Versicolor and A. niger
  • Stachybotrys chartarum: this is the most notorious type of toxigenic mold. It is also known as black mold and is known to produce a toxic chemical that causes a burning sensation in the nose, lungs, and throat and may also trigger persistent coughing spells, fever, and migraines.  

How To Tell If You Have A Toxic Mold Problem

It is important to note that toxigenic mold species don’t produce mycotoxins all the time. Hence, their presence does not necessarily mean they are producing toxins. However, since it is impossible to tell if they are or not, getting rid of molds as soon as you notice them is recommended. The following are some obvious signs that you might be dealing with a toxic mold problem:

  • A nasty smell or musty odor
  • Visible signs of mold growth, such as colored spot, rings, and patches on walls, ceilings, flooring, and furniture
  • Persistent stains after wiping off mold
  • Persistent health problems

Stachybotrys chartarum is also known as the black mold. But this is not an entirely accurate description. The color of the mold is typically a greenish-black hue. Toxic molds can also occur as grayish, brownish, or furry orange. Molds can also be wet and slimy. Since it is difficult to tell if a mold is toxic or not by merely looking at it, it is recommended that you call a professional right away as soon as you notice any of the signs highlighted above.


As long as there is enough moisture for them to thrive, molds can grow virtually anywhere. It is common for most homeowners to wonder what kind of mold is dangerous. Truth is, any kind of mold can be dangerous. Asides from the toxigenic molds that produce harmful mycotoxin and allergenic. However, pathogenic molds are equally problematic. Taking proper precautions such as dehumidifying the air, using air purifiers, and fixing moisture problems when need be will help limit the occurrence of molds and the problems they cause. If they do appear, you should get professional help as soon as possible.

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