Identifying Types of Mold – and the Potential Dangers They Pose

Elizabeth Marglin

by | Updated: August 2nd, 2022 | Read time: 5 minutes

Mold—just the sound of the word can make you flinch. And yet mold is part of the natural environment, doing its important but  thankless task of breaking down dead organic matter such as fallen leaves and dead trees. As long as it stays outdoors, mold is a wonderful thing. Indoors, however, you have a problem on your hands. Here’s what you need to know about the different types of mold – and the potential dangers they pose.

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What is mold, exactly?

Molds is an umbrella term for all species of microscopic fungi that grow in the form of multicellular filaments (which give mold its “furry look”), called hyphae. Molds thrive on any organic matter, including clothing, leather, paper, food and the ceilings, walls and floors of homes with moisture management problems.

Is there a difference between mold and mildew?

Mildew refers to certain kinds of mold or fungus. The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. While mold and mildew are both fungi that need water, oxygen, and food to live, they differ in several significant ways. Mildew is typical on wet clothes (think musty smell) and appears as patches of white or gray.

Mold tends to have a higher profile, present with dark colors such as deep green and black. and can even become fuzzy. Mildew is usually flat. They may be somewhat similar in appearance, but mildew is innocuous, causing occasional coughing fits, while mold can be toxic.

What kinds of mold are there?

The mold’s toxicity level will depend on what type it is. There are three main classifications of mold:

  1. Allergenic: Causes an allergic reaction such as eye irritation, skin irritation or asthma
  2. Pathogenic: Can cause disease, even amongst people in robust health
  3. Toxigenic: Produces substances that are toxic and can lead to dangerous or deadly health conditions

How do I know if I have a mold problem?

You can sniff out or see a mold problem. Most molds produce musty odors that are the first indication of an issue. Mold can grow anywhere there is enough dampness or a water problem. The best way to find mold is to look for signs of mold growth, water staining, warping, or to follow your nose to the source of the odor. You may have to look behind and underneath surfaces, such as carpets, wallpaper, cabinets and walls.

There are some areas of the home that are always susceptible to mold growth, and therefore need vigilant cleaning. In particular, bathrooms (especially shower stalls, bathroom tiles, and shower curtains), window moldings, the seal on the refrigerator door, and surfaces on and around air conditioners.

5 common types of mold


Appearance: Alternaria is identified by its almost velvet-like texture and dark green or brown hair-like fibers.

Classification: One of the most common types of allergenic household mold, allergenic molds produce spores that trigger allergies and allergic reactions.

Location: Alternaria typically grows in warm, damp places like bathrooms, near kitchen sinks, or by unsealed windows. Water damage can speed growth.

Dangers: Allergic reactions from mold spores include symptoms like red eyes, scratchy throat, or asthma attacks.


Appearance: Aspergillus is typically a white or gray powdery type of mold and often confused for mildew.

Classification: It’s an allergenic species of mold but can be toxic as it is also a mycotoxin producing mold.

Location: Aspergillus mold can often be found on dead leaves, compost piles and other decaying vegetable matter, stored grain, and even foods and spices. The mold spores may be carried indoors on shoes and clothing and can grow on carpeting.

Dangers: The types of health problems caused by Aspergillus include allergic reactions, lung infections, and infections in other organs. Symptoms include wheezing, coughing, chest pain and fever.


Appearance: This kind of mold has an olive-green or brown colored mold with a suede-like texture.

Classification: It’s allergenic and can trigger asthma in certain people.

Location: Found frequently in carpet, fabrics, upholsteries, wood floors, cabinets and paper. It loves humidity and grows on everything from air ducts to the back of toilets.

Dangers: This type of mold is not toxic to humans but, much like aspergillus mold, it can cause allergic reactions in some people. It has been known to cause respiratory troubles, watery eyes, sore throats, and other flu-like mold symptoms in some people.


Appearance: Bluish or greenish in color with a velvet-like texture.

Classification: It’s allergenic but with a caveat: Some species of Penicillium are extremely useful in the production of certain meats, cheeses and antibiotics like Penicillin, which comes from Penicillium chrysogenum.

Location: Penicillium typically presents as blue or green fuzzy growths. It is found in cool, damp environments. It often grows on decaying organic materials such as fruits, vegetables and vegetation. Old bread, spoiling apples and pears, and rotting plant bulbs are favorite habitats, as are water-damaged buildings—particularly in mattresses, ducts, wallpaper and carpets.

Dangers: Penicillium mold spores can easily move throughout the home in the air and be inhaled, causing respiratory problems, pulmonary inflammation, asthma, and potentially chronic sinusitis.

Stachybotrys Atra

Appearance: A greenish-black mold, this is by far the worst type of mold that you can find inside of your home.

Classification: The main fungus associated with stachybotryotoxicosis and sick building syndrome, this mold is classified as toxic.

Location: It can grow on material with a high cellulose content, such as fiberboard, gypsum board, and paper. Growth occurs when there is moisture from water damage, water leaks, condensation, water infiltration, or flooding.

Dangers: It can cause a series of very serious health issues. Commonly reported respiratory tract symptoms include nasal irritation, burning and congestion, cough, wheezing, and chest tightness. Central nervous system manifestations include headache, irritability, lightheadedness, sleeping difficulty, concentration problems and mental fatigue.In worst case scenarios, black mold can cause bleeding of the lungs and, in some cases, it can even lead to death.

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