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What Are the Worst Types of Mold?

warning-signThere’s a common misconception that ‘mold is mold’—in other words, that all mold is basically the same. The truth is, there are hundreds varieties of mold with different colors, textures and even odors.

Most importantly, some types of mold are quite a bit more dangerous than others. It’s especially important not to let the more dangerous types of mold go undetected or untreated, since they can lead to serious health complications for anyone who comes into contact with them.

We’ve written another post on some of the most common types of mold, and it’s recommended reading for anyone who thinks they may have a mold problem but isn’t completely sure.

Here, we want to focus on the absolute worst types of mold and why it’s so important to identify, assess and eradicate them before they end up causing serious damage to your household and the health of your loved ones.

What makes toxic mold?

Essentially, toxic mold is any mold that is capable of producing substances called mycotoxins. These dangerous toxins can have significant health effects including respiratory and neurological problems. Not all molds are able to produce mycotoxins, but those that can are classified as toxic molds—and these are the worst kinds of mold out there.


This toxic mold grows fast, and usually starts off with a white fuzzy appearance, like cotton. As the colony matures, the color often grows darker.

An allergic reaction or minor infection is a common response to exposure to this type of mold. For people with weakened immune systems, it’s possible to get what’s known as a “deep infection” from this mold, resulting in serious and even fatal complications.


There are actually many subspecies of Fusarium. Some are toxic and some are not. Those that are can be responsible for a variety of health complications in both people and animals. Finger and toenails are often affected, and the eyes are also at risk. Again, people with weakened immune systems are prone to more serious and infections from this type of mold, affecting the entire body if left untreated. A reddish brown, moist appearance is common for this type of mold.


This is the most common type of toxic mold in American homes today. As with Fusarium and many other species, there are hundreds of sub-species. Almost all of them cause allergic reactions, but only some are toxic in a more serious sense. These molds also vary widely in appearance and can be mistaken for other species, making them one of the most important molds to identify with proper lab testing. One notable characteristic of these molds is that they require humid air in order to flourish. Damp, dank indoor environments can easily cause mold problems of this type.


This is a particular unattractive and dangerous mold. The appearance is often black and slimy, and the health risks are equally unpleasant. This is the species people often refer to when they talk about toxic or black mold. You’d need a whole blog post to discuss the various health complications associated with black toxic mold of these variety; suffice it to say, it’s not something you want anywhere near you or your family!

There you have it!

The above is a run down of the worst types of mold you could have growing in your home. Unfortunately, even though the general appearances can be described, its very difficult (and not very wise) to attempt an ad hoc species identification. Many types of mold look alike, and the dangers of having any of the above molds in your home are great enough to merit professional inspection and lab testing. There are many types of mold that aren’t so serious—but at the end of the day, there’s no reason to take a chance!

Thanks for reading, and please feel free to leave your comments below.

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