One example of a mold 'Unfriendly' to people is a genus called Stachybotrys which is in the family of Stachybotryaceae. Because of the color normally being black this particular mold type is what has become known as toxic black mold. However, it is important to know that not all species in this genus of Stachybotrys are considered unfriendly or harmful to people.
At any rate the ones that can be toxic depends on how contact is made with the mold and a person's immune system. One person can have an allergic reaction when this touches their skin and a rash may occur depending on the sensitivity of the person.
The most extreme example can be this: A person fresh out of a lung transplant who inhales one or two spores from this genus (of the ones that are considered potentially harmful) can die. This is the extreme case where the average person inhaling a couple of spores from this genus will not be affected at all. But affects will vary from person to person based on their individual immune response and the amount of mold spores and type the person is exposed to.
Mycotoxins from mold can also play a part. These are produced by molds to 'combat' other molds in the area which I like to refer to Mold Warfare. Notice some affects below.
Long-term mold exposure, even if it doesn't cause immediate symptoms, may also lead to:
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